DESCRIPTION OF THE SNOQUALMIE QUADRANGLE
By George Otis Smith and Frank Cathcart Calkins.
INTRODUCTION. a proper introduction to the more detailed descrip a natural division line separating the eastern and streams have deeply incised their canyons. In tion of the geology of this quadrangle. western slopes as distinct topographic regions. A the highest parts of this plateau dissection has Location and area. The Snoqualmie quadrangle The oldest rocks known in the Northern Cas more obvious topographic subdivision of the area attained an extreme degree of maturity, while is bounded by meridians 121° and 121° 30' west cades are probably of Paleozoic age and repre is made by the broad .valley of Yakima River, other portions of the upland surface apparently longitude and parallels 47° and 47° 30' north lat sent volcanic products as well as sediments. Their which extends southeastward from Snoqualmie have to a large extent escaped attack. itude, and embraces 812.4 square miles. The quad characters indicate that the conditions of volcanism Pass to the eastern edge of the quadrangle, sepa In the southern half of the quadrangle the rangle is situated nearly in the center of the State and of sedimentation were remarkably similar to rating it into two elevated regions of nearly equal mountains are of a more subdued type. Steep of Washington and includes portions of Kittitas, those that prevailed during the same period in the area, which present marked differences in topo cliffs border some of the streams for short dis Yakima, Pierce, and King counties. Sierra Nevada and in British Columbia. No early graphic character. tances, but are exceptional east of the divide. Natural divisions of the State. The State of Mesozoic strata are known in this region, but during The highest peaks in this quadrangle are in the Even in their highest parts the ridges have broad Washington comprises five natural divisions, which late Mesozoic time sediments that formed sandstones extreme northern and southern parts. One of the level crests, which are taken advantage of by the are geologically as well as geographically distinct. and other rocks were laid down in portions of the "Needles" north of Glacier Lake has an altitude of principal trails. The southern part of the quad The first of these divisions is the Olympic Moun Northern Cascade area. The most important body 7512 feet, and 15 miles east of this point, at the rangle thus lacks the scenic beauty of the northern tains, which overlook the Pacific. These form of Cretaceous rocks lies near the international head of Camp Creek, an elevation of over 7000 part, and when viewed from a distance the south apparently the northern extension of the Coast boundary and represents an extension of the feet is reached on Hawkins Peak, the summit of ern ridges appear to unite in a broad, monotonous Range of Oregon, and are represented farther Cretaceous sea southward from the interior region which is a few hundred yards beyond the eastern plateau that slopes gently eastward and westward north, beyond Juan de Fuca Strait, by the heights of British Columbia. Toward the south the near edge of this quadrangle. The next highest ele from its central portion. of Vancouver Island. est known area of rocks of similar age is in the vations are near the southeast and southwest The valley of the upper Yakima, which has been East of the Olympic Mountains is the second John Day basin and the Blue Mountains of corners of the quadrangle, where the culmi taken as a division line between two topographic division, the Puget Sound basin, a notable depres Oregon. Thus central Washington may have nating points on two ridges are 6312 and 6325 provinces, is itself a conspicuous feature of the sion lying between parallel mountain ranges, and been in Cretaceous time a land area, with seas feet respectively. This distribution of the most relief. The Yakima is remarkable in that its extending beyond the boundaries of the State, both to the north and to the south. elevated points is noteworthy, since, with the low-grade valley extends well back to its head southward in the Willamette Valley of Oregon The deposition of the Cretaceous rocks seems to exception of the highest peak, they are not on waters, an easy railroad grade being maintained and northward in the sounds of British Columbia. have been followed by an epoch in which these the main divide and two of them are many to within 3 miles of Snoqualmie Pass. For a dis Its characteristic topography and geology are and older rocks were folded and uplifted. Thus miles east of that divide. The topographic map tance of 10 miles this valley approximately paral described in the Tacoma folio. was an early Cascade Range outlined, although it clearly shows that the most prominent mountain lels the main Cascade divide, which at Stampede The third division is the Cascade Range, a may be that the range had an even earlier origin. ridges in this region trend not north and south Pass is only about 1 mile distant from the edge of mountain mass trending north and south and The post-Cretaceous mountain growth was accom but more nearly east and west. The high coun the valley. The divide is here generally low and forming the most prominent topographic feature panied by intrusions of granitic and other igneous try in the northern portion of the quadrangle possesses little importance in the topography of the of the State. This line of uplift is a continuation rocks, which now constitute a large part of .the is deeply cut by tributaries of the Yakima, so region. of that of the Cascade Range of Oregon, but the mass of the Northern Cascades. During all the that, while the range continuity is not apparent, Yakima Valley is everywhere broad except for a Cascades of Washington deserve further subdivi time that any portion of this area was not covered yet the heights bordering these canyons exhibit few miles above Easton, and within this quadran sion. From Columbia River northward to the by water the rocks were exposed to the vigorous more or less uniformity in altitude. South of gle includes nearly 20 square miles of bottom land. vicinity of Mount Rainier the range resembles attacks of atmospheric agencies. Thus at the the valley of the Yakima the ridges are more A notable feature on the southwest side of the val the Oregon portion, both in topography and in beginning of the Tertiary the Northern Cascade continuous, especially the one between that val ley at Easton is a ridge rising 1600 feet above the geology, in that it consists of basaltic and andes- region appears to have been a comparatively ley and the Naches basin. The physiographic valley floor, behind which is a well-marked narrow itic lavas of Tertiary and later age. A typical rugged country, although not necessarily at a significance of this distribution of the heights valley, drained by branches of Big, Little, and portion of the eastern flanks of this part of the great elevation above sea level. will be discussed under the heading "Historical Cabin creeks, and by an unnamed creek that enters Cascade Range is described in the Ellensburg During the Eocene epoch an extensive estuary geology." Yakima River near Easton. folio. Farther north, however, older rocks appear or arm of the sea occupied the Puget Sound area The group of mountains in the northern part of The valleys of Clealum River and its several in the Cascade Mountains and the topography of and extended well over toward the present axis of the quadrangle forms a part of the important forks have wide, flat bottoms like Yakima Valley, the range becomes more varied. These geologic the range. Other large bodies of water, probably range which extends eastward across the Mount and Naches River is also bordered by broad and topographic distinctions are sufficiently impor fresh, existed in central Washington, and some of Stuart quadrangle and is known there as the meadows in portions of its course. Along the tant to deserve recognition, and on this account these may even have been connected with the Puget Wenatchee Mountains. This line of heights upper valleys in the northern part of the quad the range from the vicinity of Mount Rainier estuary. Thousands of feet of arkose sediments forms the divide between the Middle Fork and rangle, topographic features due to glaciation are northward to the forty-ninth parallel will be were deposited at this time, and in these Eocene the headwaters of the South Fork of Snoqualmie conspicuous. A noticeable example is seen in the termed the Northern Cascades. The application strata are included all the coal beds in the State River and also the divide between Yakima River character of the valley floor in the vicinity of Big of this term beyond that latitude is questionable, that a,re of economic importance. In this period and the West Fork of Clealum River. Here the Salmon Lasac, where numerous channels and basins since there is in this vicinity an abrupt change also began the volcanism that in later epochs became topography is of the boldest type, the divides have been carved in the rock, the county road fol from rugged peaks to more rounded and lower so characteristic of the province. The more exten being generally narrow, and in some places having lowing one of these side channels at some distance ridges such as occur north of the international sive basaltic eruptions, however, occurred in the knife-like crests. Extreme examples of relief of from the river. The valleys of tributary streams boundary. The areas described in the Mount succeeding epoch, the Miocene, when an area meas this character are afforded by the "Needles" in this region commonly show marked differences Stuart folio and in this folio are typical of the uring many thousands of square miles was buried between Burnt Boot Creek and the headwaters in grade between their upper and lower portions, Northern Cascades, while the southwestern por deep beneath' the flood of lava. In portions of of West Fork of Clealum River. Here spires the streams passing from broad basins with gentle tion of the Snoqualmie quadrangle presents fea this vast area sedimentation within shallow-water and pinnacles of bare rock overlook a series of grade into narrow gorges which extend to the river tures resembling those that are characteristic of the bodies immediately followed the eruption of basalt, small glaciers. Several of these divides are valley. The best examples of these hanging val Cascade Range of Oregon. Mount Adams, Mount and the Miocene epoch closed with slight tilting impassable, the precipitous character of the bor leys are on Thorp and French.Cabin creeks, which Rainier, Glacier Peak, and Mount Baker, peaks and folding of these deposits. The erosion that dering cliffs preventing ascent at any point, while enter Clealum River from the west. These creeks that dominate both portions of the Cascade Range followed the exposure of these beds and the under the narrow crest is too sharp and ragged to allow flow through rather broad valleys until they reach in Washington, are volcanic cones of later date lying rocks to atmospheric action continued until passage along the divide itself. These high peaks the brink of Clealum Valley and then cascade down than the range itself, and their presence does not the whole region was planed down to a lowland and ridges are mostly snow-capped throughout the about 600 feet through deep cuts in the valley wall. affect the subdivision here proposed. surface, possessing only slight relief. This reduc summer and, together with the cascading streams Drainage. As has been stated above, the main The fourth important division of Washington is tion of the area to what may reasonably be termed and small glacial lakes, constitute the most pictur Cascade divide crosses this quadrangle, so that the the Great Plain of the Columbia, a plateau that a peneplain marks the destruction of the earlier esque features of the scenery of the region. area includes parts of two drainage basins. The includes approximately one-third of the State and Northern Cascades as a mountain range, but Somewhat in contrast v», with such ridges<-) are others streams tributary to the Columbia River are extends southward into Oregon and eastward into toward the close of Tertiary time, probably, to the east and southeast. Goat Mountain, and Yakima River and its various branches, the largest Idaho. The Ellensburg quadrangle, described in this leveled surface was gradually uplifted to especially the ridges between the Middle and West of which are Clealum and Naches rivers. The folio 86, lies in the border land between the Colum form the present Cascade Range. This uplift at forks of Clealum River, between Keechelus and streams tributary to the Puget Sound drainage bia Plain and the Cascade Range. its very beginning inaugurated fresh attacks upon the two Kachess lakes, and between the Kachess include the headwaters of four rivers Snoqualmie, The mountainous district bordering the Colum the rock masses by the streams, and is so recent lakes and Clealum River, are characterized by a Cedar, Green, and White. bia Plain on the north and traversed by the inter that streams and glaciers have as yet succeeded somewhat different type of upland topography. The eastern and western drainage basins exhibit national boundary constitutes the fifth natural only in giving to the range an extremely rugged Viewed from below these present the same steep a marked contrast in stream grades. The Yakima division of the State. It includes the Colville relief. slopes, often with bold walls of rock rising 2000 and its-larger tributaries are as a rule characterized Mountains, which apparently represent the south or 3000 feet from the lake or river, and Goat by low grades, but the westward-flowing streams ern continuation of higher mountains in British TOPOGRAPHY. Mountain presents on its southeastern face an descend much more rapidly. Thus it happens Columbia. Relief. The Snoqualmie quadrangle lies in the almost unbroken rock wall over 3500 feet high. that, although the divide between the two drainage General geology of the Cascade Mountains. heart of the Cascade Range and includes about 50 Yet on the summits of these ridges there are basins lies near the western margin of the quad The geology of a limited area like the Snoqualmie miles of the main divide between the Puget Sound level stretches of forest or grassy meadow, and rangle, the lowest point in the area, 1400 feet, is quadrangle can not be fully understood without drainage and the streams tributary to the Columbia. traces of old Indian trails emphasize the con in the northwest corner. Also, while the descent some general knowledge of the province of which Yet this divide is not the most important element trast between these heights and those of the other of the Yakima is only about 1000 feet from its it is a part. A brief outline of the geologic his in the relief of the quadrangle, since it is to a large type. This northern area, then, can be briefly source at Snoqualmie Pass to its junction with tory of the Cascade province will therefore serve as extent an inconspicuous feature, and does not form described- as a plateau region in which the larger Clealum River, a distance of over 25 miles, the South Fork of the Snoqualmie, flowing westward are sandstones and shales, deposited as sands and described when the formations are discussed. The Lake. Locally these rocks show a considerable from the same point, descends 1200 feet in a dis muds in large inland lakes, or lavas and beds of oldest formations in this region are the Easton proportion of graphite and at one place they have tance of about 5 miles. A somewhat similar grade tuff, erupted from openings in the earth's crust. schist, the Peshastin slate, and the Hawkins vol been prospected for coal, which there is, however, is shown on Green River, and this difference between Associated with these are also intrusive rocks of canic rocks. Of these the oldest and most no reasonable hope of finding. the eastern and western slopes is made even more Tertiary age. altered the Easton schist is a metamorphic As studied under the microscope, the Easton rocks fall into apparent by the different types of railroad engi The difference in age between these two groups formation that probably comprises both sedi two principal groups the quartz-mica phyllitic schists and the amphibolitic schists, and the petrographic characters of neering east and west of Stampede tunnel, on the of rocks is considerable. The older rocks had been mentary and igneous rocks; the others, although each will be described in somewhat general terms. Northern Pacific. long exposed to the influence of the atmosphere somewhat altered, are plainly sedimentary and The phyllitic schists have for their chief constituents quartz volcanic, respectively. The pre-Tertiary igneous and muscovite. They are composed of thin laminge, alter The rivers and streams of this quadrangle all and carved by streams into hills and valleys when nately quartzose and micaceous, along which the rock splits benefit by the heavy annual precipitation of the the first deposits in the Eocene waters were laid rocks that are intrusive in these formations are readily. The mica is very finely divided and gives a silvery Cascades. The seasonal character of this precipi down over an uneven surface composed of rocks peridotite (now largely altered to serpentine), the sheen to the surfaces of the layers. The colors, which, as already noted, vary from blue-black in certain graphitic tation is somewhat counteracted by its storage in widely differing in character. This is what is Mount Stuart granodiorite, and a quartz-diorite varieties to blue-gray and grayish green, are dependent upon the high mountains in the form of snow, banks of meant by the statement that there is at the base which is probably older than the granodiorite. the - presence of graphite and ehlorite. The microscope All but the last of these formations also occur reveals, in addition to the constituents above noted, a little which, during ordinary seasons, persist late into of the Eocene sandstone a marked unconformity feldspar, with some accessories, as magnetite and zircon, in the summer and in many places throughout the representing an erosional interval. In the follow in the Mount Stuart quadrangle and are described trifling amounts. year. Two small glaciers are included within this ing portions of this descriptive text all of these in folio 106. The amphibolitic schists, darker green in color, do not show such marked lamination as the phyllitic schists, but they quadrangle, and these, together with others imme formations, both pre-Tertiary and Tertiary, will be EASTOX SCHIST. exhibit distinct cleavage, and a roughly parallel arrange diately north of the quadrangle, are tributary to described with more detail, and these descriptions ment of amphibole prisms is visible megascopically. Their present texture has evidently been determined by meta West and Middle forks of Clealum River, serving will be followed by an outline of the geologic his General character and occurrence. The Easton morphism, which has obscured their original texture. Their to keep up its discharge in the summer months. tory of the region, which is an interpretation of the schist comprises light-green and bluish, banded essential constituents, as shown by the microscope, are green The larger of these glaciers is directly exposed to record afforded by the rocks. phyllitic schists and darker green schists rich in hornblende, lime-soda feldspar, usually a little quartz, and more or less epidote and ehlorite. The last two are especially the sun, and its existence is therefore the more In the texts of folios of the Geologic Atlas it has hornblende. The name given to the formation abundant in the fine-grained schist at the head of Little remarkable. Although small, these glacier rem been customary to separate the descriptions of the is that of a small town in Yakima Valley, close Kachess Lake. Magnetite, apatite, and titanite occur as nants present all the characteristics of true glaciers sedimentary from those of the igneous rocks. In to which it is well exposed. It includes sedi rather abundant accessories. and are traversed by crevasses, on whose walls the the present case, however, the order of treatment mentary and igneous rocks, now highly meta The Easton schists, like several later formations banded structure of the ice can be seen. The work will be based upon succession alone. This deviation morphosed. A characteristic feature of the for in the quadrangle, seem originally to have been of the ice streams of which these are the survivors from the usual practice is considered desirable in mation as a whole is the extreme alteration composed of interbedded sedimentary and volcanic can be traced along all the valleys in the northern view of certain facts that are peculiar to this prov produced in it by heat and by mountain-mak rocks a conclusion reached chiefly by petrographic half of the quadrangle. ince. Several of the formations here described are ing pressure. These agencies have produced new study. The phyllitic schists, judging by their Culture. The total population of this quadran of composite character, being in part of sedimentary "metamorphic" minerals as mica and horn lamination and by their chemical composition, gle in 1900 was about 600. This is probably and in part of volcanic origin. Most of the sedi blende and characteristic schistose and crumpled which is similar to that of sandy clay, appear to nearly evenly divided between King and Kittitas mentary formations are not widely distributed but structures, the latter being especially evident in the have been derived from sediments. The amphib counties, and is practically confined to the imme rather represent local deposits in a region where laminated sedimentary rocks. The bedding and olitic schists, on the contrary, are chemically related diate vicinity of the line of the Northern Pacific igneous activity frequently interrupted sedimen schistosity of these rocks are in general highly to the basic igneous rocks. In clastic rocks the Railway. Easton and Lester are the only villages. tation. The rapidity with which one geologic inclined, and very frequently vertical. The ferromagnesian constituents are washed away, leav Ronald was formerly an important mining town, process succeeded another is the most noteworthy intense metamorphism of the Easton formation ing a dominant proportion of the more resistant but is nearly deserted now, the center of the coal characteristic of the history of the province, and is an indication of its great age and the chief minerals, as quartz and the acid feldspars, with mining industry being at Roslyn, immediately east since the rock formations constitute the record of criterion for its distinction from later formations. more or less argillaceous material, which becomes of the edge of this quadrangle. that history, the strict separation of the sedimen The Easton schist is exposed in three zones. altered chiefly to mica. Rocks so rich in ferromag Agriculture and the lumber industry support tary and igneous rocks would tend to obscure the The first of these extends southeastward from nesian constituents as these amphibolites are there most of the permanent inhabitants. Agriculture record. Easton in a conspicuous ridge which has been fore, in all probability, igneous. As to whether is practiced only on a limited scale, and is con carved from the schist. Parallel with this and they are volcanic or intrusive, there is no perfectly fined to the valleys of the Yakima and Clealum. PRE-TERTIAEY ROCKS. about 2 miles south of it is a second zone of clear evidence, but since they are fine grained and During the summer months large bands of sheep Age and succession. The precise geologic age of Easton schist and of other pre-Eocene rocks, in the form of layers it seems more probable that graze in the elevated region bordering the lower the pre-Tertiary rocks can not be determined, owing from which is carved another prominent ridge. they are volcanic. Clealum Valley and in the southern half of the to lack of paleontologic evidence, but the very The third zone of this schist comprises three large quadrangle east of the divide. marked unconformity by which they are separated areas in the north-central part of the quadrangle. PESHASTIN FORMATION. This quadrangle includes the only wagon road from the overlying Eocene strata proves conclu All of these zones extend in a northwest-southeast General character and occurrence. -The Peshas crossing the Cascade Range in Washington, the sively that they are pre-Tertiary. This uncon direction. tin formation is best exposed on the creek of that Snoqualmie Pass road, which is therefore an impor formity, moreover, represents a very long time Lithology. The hard and resistant Easton name in the northeastern part of the Mount Stuart tant route, although in many years it has been interval. The Eocene beds rest not only upon schist affords extensive exposures, the best of quadrangle. In the Mount Stuart folio (No. 106), blocked with snow except during the summer the eroded edges of older sedimentary strata which occur on the escarpment south of the the formation is described as consisting chiefly of months. Another county road leading well into but also upon the granular igneous rocks that Taneum Creek basin, in the canyon of Little dark-colored slate interbedded with subordinate the heart of the range follows Clealum River. By were intruded into those sediments. Intrusive Creek, and on the bold wall east of Little amounts of grit, conglomerate, chert, and lime these two routes many prospectors reach the Sno rocks of this kind must have consolidated far Kachess Lake. The observed exposures, how stone, the last forming lenses of very moderate qualmie Pass, Gold Creek, and Camp Creek dis beneath the surface, so that their presence at ever, constitute only parts of the whole forma extent. tricts, where they work during the summer months the base of the Eocene strata shows that this tion, and owing to the impossibility of working In the Snoqualmie quadrangle, on the ridge and even throughout the greater part of the year. unconformity records the removal by erosion of out the structure of these intensely deformed between Taneum Creek and Naches River, there a cover of considerable thickness a process which rocks no satisfactory correlations can be made, is one main area of dark slate similar to the typi DESCRIPTIVE GEOLOGY. in turn implies that a long interval of time had nor can the succession of beds be accurately cal Peshastin, and smaller areas occur between the . STRATIGBAPHY. elapsed between the igneous intrusions and the determined. Therefore only the general charac headwaters of Taneum and Manastash creeks. ' In beginning of Tertiary time. ter of the formation as seen in the field will be the northeast quarter of the quadrangle there are General features. The Snoqualmie quadrangle The great difference in appearance between the stated. three small areas of rocks which it seems best to is a remunerative field for geologic investigation. schists and slates and the Eocene sandstones is In the region about the headwaters of Taneum refer to this formation. One of these, in the basin Here both the oldest and the youngest rocks thus more striking to the casual observer than the and Manastash creeks the Easton schists are of Fortune Creek, is an area of metamorphosed sili far discovered in the Northern Cascades are exposed unconformity just described. This contrast is due chiefly aniphibolitic. The amphibolitic schists are ceous rock, such as might be derived from some and the structure of the Cascade Range is well to a difference in degree of alteration between the greenish gray to almost black in color and suffi phase of the Peshastin formation, which occurs in exhibited. The formations, which are represent rocks of the two groups, and indicates that the ciently coarse grained to enable the hornblende to force immediately east of the edge of the quad ative for much larger areas, may be separated time interval between the deposition of the pre- be easily recognized. They do not show much rangle. Another is a small area of impure lime for convenience into two classes, the older or pre- Eocene rocks and that of the Eocene sediments crumpling and break into flat. leaves or slabs. stone and calcareous shale northwest of Clealum . Tertiary, and the younger or Tertiary. This classi was not only great but eventful. It must have Schist of this character forms the upper part of the Lake, but as these rocks are not near any exposure fication is natural in view of the great unconformity included several momentous episodes of defor cliff* south of Taneum Creek, but the lower part of characteristic Peshastin slate, their reference to at the base of the Eocene, although the difference mation and intrusion as well as one or more is composed of a lighter green, more siliceous rock. that formation is somewhat tentative. The third between the rocks of these two groups is not so periods of long-continued erosion. Thus it may Farther east on the same ridge, at the head of the area is a narrow band of metamorphosed limestone apparent in this quadrangle as it is farther east, be reasonably supposed that the period of defor North Fork of Manastash Creek, are some fine at the head of Boulder Creek. in the Mount Stuart quadrangle. In both groups mation, intrusion, and erosion included all of grained, olive-green rocks with small white spots Relations. The belief that the Peshastin forma the rocks are varied in composition and in kind. Mesozoic time and that the oldest rocks in this that look like altered porphyritic feldspars. tion is considerably younger than the Easton There has been no definite determination of the area are of Paleozoic age. This conjecture is The zone lying next north is formed in greater schist is not supported by such definite evidence age of any pre-Tertiary formation, but several of further warranted by the fact that similar rocks part of siliceous and phyllitic schists, gray-green as Avould be afforded by an exposure of typical the Tertiary formations carry fossil plants that in British Columbia, the Blue Mountains of Ore and bluish in color. Such rocks are exposed on Peshastin slate resting with distinct unconformity afford a basis for fixing their exact age. gon, and the Sierra Nevada of California are the railroad above Easton, on the little island in upon the Easton schist. At a point between Tan Among the pre-Tertiary formations intrusive known to be Paleozoic. Kachess Lake, and in the low hills south of Nelson. eum and Manastash creeks, where the boundary and metamorphic rocks predominate that is, rocks The age of the pre-Tertiary intrusives can only Some hornblende schists also occur in this zone, between these two formations is best seen, the con which acquired their present character deep below be a matter of conjecture. That they are Mesozoic, especially in its southern part. tact plane is a fault, and nowhere is a normal the surface of the earth. The intrusives were con however, can be considered probable, since in Cali In the northernmost zone one of the most abun contact of superposition well exposed. solidated from bodies of molten material forced up fornia and Oregon that age has been assigned to dant rocks is an olive- to blue-green schist, fine At the occurrence near Clealum Lake the cal from below and the metamorphics were formed by granodiorite and serpentine similar to those occur grained and tough, which is extensively developed careous rock overlies Easton schist but'is separated , the alteration, through the agency of heat and ring in this area. near the head of Little Kachess Lake. In this from it by a layer of metamorphosed volcanic mountain-making forces, of sedimentary and igne Although the precise geologic age of these pre- northern district there is also a large amount of rocks. Here there is a distinct unconformity, for ous materials. The Tertiary rocks, on the other Tertiary formations is thus in doubt, their ages thinly laminated and intensely crumpled bluish the schist is vertical while the limestone and shale hand, are chiefly of the kind formed at the surface, with respect to one another may be determined schist, which is typically developed in areas north have a dip of 45°. Of course the doubt attending such as sediments and volcanic deposits. These by their obvious geologic relations, which will be west of Clealum Lake and north of Little Kachess the reference of these rocks to the Peshastin for- *
3
mation diminishes the value of this observation. HAWKINS FORMATION. what favors the belief that the Hawkins is the the first type of topography has somewhat widely Thus, it follows that the principal evidence as to General character and occurrence. The Haw younger. spaced joints, like those common in granite. The the relative age of the two formations is almost kins formation consists of volcanic rocks, mostly These two pre-Tertiary formations are provi rock in which the second type is developed is wholly the low degree of metamorphism shown by basic and dark colored and of the general type sionally assigned to the Carboniferous system. divided by innumerable fissures, generally curved, the Peshastin slate as compared with that shown often termed greenstones. These rocks include This assignment rests wholly upon their tentative intersecting and anastomosing irregularly. Where by rocks in the Easton schist that are believed to amygdaloidal lavas, breccias, and tuffs, which have correlation with somewhat similar rocks in other the fissures are most numerous the rock can be have been of similar original composition. This been considerably altered but not so much so as to parts of the Pacific province which are known crumbled with the fingers into minute flakes, but difference in degree of metamorphism is so marked obscure wholly their original character. The most to be of Carboniferous age. The Hawkins and embedded in the fissured material are abundant as practically to demonstrate that the Easton rocks obvious feature of the Hawkins rocks is their tend Peshastin formations, taken together, bear a strik bowlder-like masses of firm and comparatively underwent the larger part of their alteration before ency to weather into rugged slopes with crest lines ing resemblance to the "Cache Creek series" of fresh rock. These masses are not well rounded, the Peshastin formation was deposited. marked by pinnacles and spires. This character British Columbia, a series which in its eastern but are bounded by facets. Their surfaces are of It is evident that exposures which so imperfectly istic topography is well exemplified on the upper development includes argillites with intercalated green translucent serpentine and are usually stri show geologic relations can furnish no grounds for part of Hawkins Mountain, where the formation is limestones, sandstones, and conglomerates, together ated and polished, so that they glisten in the an estimate of the thickness of the formation. This typically displayed. with a large amount of contemporaneous green sunlight. is also true of exposures in the adjoining Mount The distribution of the Hawkins formation in stones. Moreover, slates and limestones with asso The remarkable schistose structure which is Stuart quadrangle, where complicated structure and the Snoqualmie quadrangle is similar to that of the ciated volcanics supposed to belong to that series developed in parts of the serpentine, and which extensive intrusion by igneous rocks prevent any Peshastin. Near the northeast corner there are extend southward into Washington along Okano- appears also in similar rock found elsewhere, has measure of stratigraphic thickness. The lithologic three areas, of which the easternmost, extending gan Valley. Here the altered basic lavas and been studied by observers in other fields and shown differences between the various areas referred to into the Mount Stuart quadrangle, includes Haw pyroclastics overlie the limestone and slate, and to be a result of the conversion of the original non- the Peshastin suggest, however, that these are rem kins Mountain and affords the most typical expo if the correlation is correct it implies that the hydrous magnesian silicates, olivine and enstatite, nants of a formation whose thickness possibly sures. The areas of greenstone in the southeastern Hawkins greenstone is younger than the Peshastin to the hydrous magnesian silicate, serpentine. The measured thousands of feet, and that some of the part of the quadrangle are referred to this forma formation. process is hydrothermal in its nature, and may exposures represent the upper part and others the tion from their resemblance to the rocks of the The relations at the occurrence near Clealum have been accomplished in this region by waters lower part of that formation. northern areas both in this and the Mount Stuart Lake, however, appear to be not in accord with heated by the intrusion of the Mount Stuart The age of the Peshastin formation and its pos quadrangles. The small area of volcanic rock the foregoing evidence, Here the volcanic rock granodiorite. In contrast to weathering, it is sible correlation with similar beds in other areas northwest of Clealum Lake has been mapped as underlies the calcareous shale and the two rest deep seated; and it is attended, moreover, by a will be discussed later in the description of the belonging to the Hawkins formation, but, as will unconformably upon the Easton schist. It has considerable increase in volume. Inevitably, there Hawkins formation. be indicated in a later paragraph, this reference is been mentioned above, however, that the lava and fore, it developed enormous expansive stresses which Lithology. The dominant rock in the main area made with some doubt. breccia here exposed is partly rhyolitic and unlike produced the multitudinous fissures in the rock and of the Peshastin formation in this quadrangle is a Lithology. Hawkins Mountain is carved from the typical Hawkins greenstone, so that these may the movement of fragments upon one another, dark-gray to black slate, plainly derived by indu a typical breccia composed of black, reddish, and be some earlier volcanic rocks which lie at the base shown by the characteristic slickensiding. ration and alteration from a somewhat carbona greenish angular fragments cemented by a red and of the Peshastin formation and are distinct from The fact that this alteration has proceeded much ceous mud. This slate is mostly homogeneous green matrix. At other localities the rocks com the later eruptives which overlie the sediments. farther in some areas than in others closely adja and lacks conspicuous banding, although it con posing this formation are dark green, either mass In view of all the evidence this is perhaps the cent is strongly impressed upon the observer in tains some thin arenaceous layers. Cleavage, ive or brecciated, and at some places they are most satisfactory explanation of the occurrence, the field and calls for explanation. It is likely while not very well developed, is generally pres aphanitic, so that their igneous nature is not but provisionally these pre-Tertiary volcanic rocks that before the serpentinization certain zones in ent, being usually parallel to the bedding, but in apparent. are mapped as belonging to the Hawkins formation. the peridotite were fissured by orogenic agencies, some cases inclined to it. Under the microscope, all these rocks show tex and that, numerous passages for the circulating hot PERIDOTITE AND SERPENTINE. In the small area south of Fortune Creek the tures characteristic of lavas or other volcanic waters thus being provided, hydration was far more rock has been highly altered by the peridotite which deposits. They have been considerably altered, General character and distribution. Peridotite is rapid and complete in these zones than elsewhere. surrounds it, and the formation here includes green the alteration resulting in the production of sec a dark-colored, granular, intrusive rock whose chief This extensive serpentinization occurred in pre- and bluish siliceous schist, together with some ondary minerals, such as hornblende, calcite, constituent is olivine. Olivine is very susceptible Tertiary time, for a peculiar phase of the Eocene impure quartzite. At the occurrence near Clea- epidote, chlorite, and quartz. Yet the character to alteration by hydration to the mineral serpen basal conglomerate, to be described later, contains lum Lake the rock is a thin-bedded and fine of these alteration products, together with rem tine, and when this change has proceeded far the faceted and striated bowlders of serpentine exactly grained gray limestone interbedded with calcareous nants of augite and plagioclase crystals, indicates altered peridotite is called serpentine. Naturally, similar to those mentioned above as occurring upon shale and shaly sandstone. The sandstone, when approximately the original composition of the rocks showing various degrees of serpentinization the surface today. Inasmuch as these owe their studied microscopically, appears to be tuffaceous. rocks and, together with abundant traces of grade into one another and are not to be separated form to shearing within the peridotite mass, this One exceptional phase of the Peshastin forma ophitic texture, shows that the Hawkins lavas in areal mapping. In the Snoqualmie quadrangle action and the hydration which caused it must tion and its mode of occurrence requires special were prevailingly basaltic. there are intrusive masses which were originally have occurred before the accumulation at the mention. Within the peridotite or serpentine In the area near Clealum Lake, however, the peridotite but are now all serpentinized in some Eocene surface of the bowlders and detritus form areas or in the areas of Peshastin rocks near rocks appear to have been more acid in compo degree. An area of these rocks in the northeast ing the conglomerate. the contact with the serpentine, at a number of sition. Here there is a green, spotted schist, corner of the quadrangle has an extent of several . The freshest specimens of this serpentine, which localities in the Mount Stuart quadrangle, there wliich might have been derived from a basic square miles, comprising the western portion of best show the original character of the rock, are are ledges, only a few feet across, of a bright-yel tuff or lava, but above this are some porphy- two belts that extend nearly across the Mount obtained from the massive-jointed phase and the low or light-red rock with rough, ragged surfaces. ritic rocks of .andesitic composition and a purple Stuart quadrangle. The peridotite also continues bowlder-like masses of the schistose phase. Such These ledges have a general east-west trend, and flow breccia, with phenocrysts of quartz and feld northward beyond the boundaries of the two quad material consists mainly of a dark-green waxy- are locally known as the "nickle ledge" or "por spar, which is rhyolitic or dacitic. Locally this rangles, covering an area in this region that prob looking substance, in which are embedded a vari phyry dike." Owing to their hardness they material is sheared to a purple, slaty rock that ably exceeds 100 square miles. In the complex able quantity of lighter olive-green crystals with weather out more prominently than the sur shows no igneous features. of metamorphic rocks in the southeast corner of bright satiny lustre. Locally tMe rock contains rounding rocks, and their characteristic rugged Relations and age. The relations of this for the quadrangle there are dikes of serpentine that many irregular veinlets, composed of greenish- erosion forms and bright colors make them easily mation to the Easton schist are nowhere well trend northwest-southeast, eight of which are large white silky fibers. recognized at considerable distances. exhibited, yet the lesser degree of metamorphism enough to be represented on the map. Microscopic examination shows that the rock was origi The principal occurrences of this peculiar rock of the Hawkins greenstone is believed to indicate Relations. In the northern area the peridotite nally composed essentially of olivine with less enstatite, and that it therefore belongs to the variety saxonite. Remnants in the Snoqualmie quadrangle are on the eastern that it is of later ages than the Easton schist. is plainly intrusive in the Peshastin and Hawkins of both these minerals are found in the majority of slides, edge in the upper basin of Boulder Creek, but of There is a similar lack uf direct evidence regard formations, but is in turn intruded by the' Mount but both are largely replaced by characteristic varieties of these only one, which continues eastward into the ing the relative ages of the Hawkins and Peshastin Stuart granodiorite. These relations, of course, serpentine, whose origin generally can be recognized even when the alteration is complete. That derived from olivine Mount Stuart quadrangle, is extensive enough for formations. In the southeastern areas the two fix its relative age, while the fact that it is directly has the "mesh structure," and that derived from enstatite mapping. Near the mouth of this creek large formations are intimately associated and so intri overlain by Swauk conglomerate with serpentine has the parallel-fibrous or "bastite structure," both familiar to students of petrography. The amorphous-looking waxy blocks of the typical yellow rock may be seen. cately folded together that their areal separation bowlders shows that it was denuded before the serpentine is of the first variety, and the satiny light-green for the purpose of mapping is difficult. The beginning of the Tertiary period. The dikes in crystals are chiefly of bastite. Examined microscopically the rock exhibits no structures boundaries drawn between them are only approx the southern part of the quadrangle are likewise A chemical analysis of the rock by Dr. Hillebrand, pub that afford any clue to its origin, and the only determinable lished in the Mount Stuart folio, shows a high percentage of constituents seen are carbonates and iron oxide. Chemi imately correct, for the Peshastin areas include intrusive in the Peshastin and Hawkins forma magnesia, considerable iron oxide, and a comparatively low cally it is a siliceous dolomitic rock containing considerable subordinate amounts of infolded Hawkins green tions, and although their relation to the granodio silica content. Alumina, lime, and the alkalies occur in very iron. A specimen analyzed in the laboratory of the United subordinate quantity. The percentage of water is notably States Geological Survey contained only .08 per cent of nickel stone, while within the Hawkins areas there are rite is not seen they probably belong to the same high, being nearly 14 per cent. oxide (NiO), which is even less than the percentage of nickel masses of slate too small to be separated on the epoch of intrusion as the peridotite of the main in the serpentine. QUARTZ-DIORITE. Two explanations may be given of the origin of this "nickel map. It is evident that such a complex will not area. ledge:" (1) The bands may represent mineralized zones in yield very definite data as to the relative ages of Lithology. The peridotite as seen in the field General character and occurrence. The quartz- both the serpentine and the slate, or (2) they may have been its members. shows great variability in color and in mode of diorite is lithologically distinct from any other originally calcareous beds or lenses belonging to the Peshas tin formation, in part included within the intruded perido On Sheep Mountain, in the Mount Stuart weathering. Its erosion forms are of two con rock that forms a considerable mass in this quad tite, in part situated along its contact, and thus in a position quadrangle, the two formations are in appar trasted types. In some localities, as along the rangle. It is a gray granular rock, composed to have been subject to alteration by this magnesia-rich igne essentially of plagioclase, quartz, and hornblende, ous rock. The latter hypothesis is the one which is better ently conformable contact, with a low dip, and south side of Fortune Creek, the rock is carved supported by the relations observed. Limestone lenses such this relation was interpreted as proving the over into bold and massive features and forms a talus with a distinctly recognizable, though not very as are called for by this hypothesis occur within the Peshas lying Hawkins greenstone to be the younger of great angular blocks, while elsewhere, as upon marked, secondary foliation. It occurs in but tin areas, though they are not known at the serpentine con tact. Here, however, the peculiar magnesian rock does occur, rock. This determination seems to accord with the south side of Mount Hawkins, it forms smooth one area, which lies southeast of Easton. It is and just beyond the eastern edge of this quadrangle, on the the structural relations suggested by the general slopes and gently rounded summits covered with a resistant rock and for the most part is exposed ridge next south of Hawkins Mountain, a ledge of this mag on elevated ground. Its general characters can nesian rock runs parallel with the bed of limestone within distribution of the two rocks in that quadrangle. fine shingle. The color of the massive rock on the slate series, the relationships plainly indicating that the Inasmuch, however, as all the exposures of these fresh fractures is olive-green, but the weathered be studied fairly well in the field, although it is altered condition of the former rock is directly dependent on rocks consist of masses surrounded by the large surfaces are usually dark green or reddish brown, largely weathered at the surface. The marginal the proximity of the serpentine, with which it is partly in contact. The association of the slate with the magnesian peridotite intrusions, too much dependence should while the shingly serpentine shows paler tints of portions of the mass afford more satisfactory rock is therefore believed to justify the mapping of the latter not be placed upon apparent relations. The bluish green. exposures of fresh rock than portions of its inner as also belonging to the Peshastin formation. The enrich ment of the calcareous rock with magnesia may have occurred areal distribution of the two rocks in the south These different modes of weathering express dif part. at the time of the intrusion of the peridotite or later. ern part of the Snoqualmie quadrangle also some ferences of internal structure. The rock showing Relations and age. Many exposures show clearly Snoqualmie. that the quartz-diorite is intrusive into the Easton excludes a correlation with the Snoqualmie grano very locally, in the granodiorite of the masses that volcanics were deposited after a portion of the schist, the only pre-Tertiary formation with which diorite, which is of Miocene or post-Miocene age. lie on either side of the quartz-diorite. These dif Swauk was eroded, and its total original thick it is in cpntact. East of Goat Peak it is clearly On the other hand, all the relations observed are ferences are so sharp that representative speci ness at this locality must therefore have exceeded overlain by fine conglomerate of the Naches for in harmony with the reference of these masses to mens of the rocks would never be confounded 5000 feet. East of Kachess Lake and north of mation. There are no other data bearing upon its the Mount Stuart granodiorite. by a petrographer. Little Kachess the thickness of the formation age, so that the period of its intrusion can be stated The irruption of the granodiorite into the Peshas The geologic relations of the quartz-diorite and exposed between the Easton schist and the only as post-Easton and pre-Tertiary. It is well tin clay slates east of the head of Little Creek has the granodiorite do not preclude their correlation, Kachess rhyolite is much less. Since it may to note however that the rock may be older than resulted in their metamorphism. The sedimentary but on the other hand they do not preclude the have been eroded here, as elsewhere, before the the Peshastin slate. .On the other hand, the pos rocks here have a sparkling crystalline appearance hypothesis that the two rocks represent intrusions overlying volcanics were laid down it is difficult sibility of correlating it with the Mount Stuart and contain little knots of prismatic form. When of widely different age. The granodiorite is intru to determine how far this apparent thinning may granodiorite might suggest itself to one familiar the rock is examined in thin section, it is seen to sive in the Peshastin and Hawkins formations, be due to erosion. It is probable, however, in with that rock and its relations. The reasons contain developed in it a large proportion of biotite but the quartz-diorite is found in contact only view of the absence of strong unconformity with for not making this correlation can be pre and scattered porphyritic crystals of brownish- with the older Easton schist, and may be pre- the rhyolite, that no great volume of sediments sented more clearly after the relation of the yellow andalusite. Peshastin. The gneissic structure of the quartz- was ever deposited at these localities, which were Mount Stuart granodiorite and the lithology of Lithology. By Lindgren's definition granodio diorite supports this conjecture, for it may indicate therefore, perhaps, near the final shore lines of the both rocks have been discussed. rite is a granular rock consisting essentially of that the rock participated to some extent in the basin in which the Swauk was laid down. The irruption of the quartz-diorite into the plagioclase, orthoclase, and quartz, with biotite or great disturbances which the Easton schist suffered Lithology. The Swauk formation consists of Easton schist has produced distinct metamor- hornblende, or, as is usual, both; the plagioclase before the Peshastin formation was laid down. conglomerate, sandstone, and shale. Of these phism. On the south side of Yakima Valley markedly, although in variable degree, predominat rocks the most abundant is sandstone. The con the diorite is in contact with green schists, prob ing over orthoclase. This rock constitutes a well- TERTIARY SYSTEM. glomerate is confined mostly to the lower part ably of igneous origin. In these rocks it has defined type, probably the dominant one in the EOCENE SERIES. of the formation, and the shale is found inter- produced a coarser crystallization, but appar great batholiths of the western Cordilleras. Eocene rocks occupy nearly one-half of the Sno bedded with both conglomerates and sandstones. ently no new minerals, the contact rocks being The masses mapped as Mount Stuart granodiorite qualmie quadrangle. In order of age, the forma The base of the formation is usually conglom medium-grained hornblende-schists. The intruded are composed mainly of a rock corresponding in all tions comprised in the Eocene series are the Swauk, eratic, although at a number of localities finer rock contains apophyses of the intrusive, which respects to the type as defined, but comprise a the Naches, the Kachess, the Teanaway, the Roslyn, sediments rest directly on the older rocks. In have been sheared subsequently to the intrusion. small amount of more basic rocks, which are gen and the Manastash. The Swauk, Roslyn, and the latter case the sandstone or shale is composed This fact, combined with the basicity of the dio erally developed at the margins of the masses. Manastash consist of sedimentary rocks alone. of material derived from the underlying rock; for rite near the contact and the chemical relation Megascopic examination of the granodiorite shows The Naches formation includes sandstone and example, greenish-yellow sandstone containing ship of the two rocks, makes it sometimes difficult that its chief constituent is white feldspar, which basalt. The Kachess and Teanaway are impor fragments of serpentine is found in contact with to determine precisely the position of the contact. is accompanied by quartz in moderate quantity and tant volcanic formations, the first consisting chiefly the serpentine. The coarsest phases of the basal Lithology. The rock forming most of the mass by moderate and sensibly equal amounts of horn of rhyolite, the second chiefly of basalt. Since the conglomerates are likewise very local in their is a rather coarse-grained, light-gray quartz-dio- blende and biotite. The quartz is in rather small separation of sedimentary and igneous rocks so occurrence, and in their composition often bear rite-gneiss. Its chief constituent is snow-white anhedral grains. Of the feldspar there can be intimately connected is impracticable, these six a definite relation to the underlying formation. feldspar, but it contains considerable dark-green recognized, megascopically, two varieties, (1) pla formations will be described in the order of age. The serpentine conglomerate is composed of hornblende in large prisms having a rudely par gioclase, which occurs in partly idiomorphic indi slickensided bowlders, such as occur abundantly SWAUK FORMATION. allel arrangement. Biotite is absent and quartz viduals on which striations may be seen, and (2) in some parts of the peridotite areas, with a is not abundant or conspicuous. unstriated orthoclase, which occupies interstices and General character and distribution. The Swauk scarcely noticeable admixture of small pebbles Near the irruptive contacts there is considerable in some places forms large poikilitic individuals formation consists of sedimentary strata, chiefly of slate and other rocks, the whole cemented variation from this principal type. Here occur that inclose plagioclase as well as hornblende and sandstone, with some conglomerate and shale. by finer detritus derived from the serpentine. phases very rich in hornblende, in which the biotite, these also approaching idiomorphism. These rocks are but slightly indurated and are not Such a phase of the basal conglomerate is found gneissic banding is more conspicuous than in the Titanite is an accessory that is visible megascop conspicuously altered. The beds commonly dip in the valley of the North Fork of Clealum lighter colored rock. There are also some rocks ically in some specimens of the rock. at moderate angles, although they are steeply River, where the conglomerate is associated with that appear to be sheared diorite-porphyries, show Under the microscope the additional common .tilted and are even vertical at a few localities. a shale composed of serpentine and magnetite, ing rounded phenocrysts of feldspar in a schistose accessories magnetite, apatite, and zircon are The formation is named for Swauk Creek, in representing residual material from the rock hornblendic base. visible in small quantities. The hornblende is the Mount Stuart quadrangle, where it is exten directly beneath. These local conglomerates mark Under the microscope the feldspars are found to be mainly of the common green variety, and the biotite is a sively exposed. the position of shallow bays, the sediments in plagioclase, belonging for the most part to the species labra- deep greenish brown. The orthoclase is not per- In the Snoqualmie quadrangle its development which were derived from the region immediately dorite and andesine. Quartz is present in somewhat variable thitic. The plagioclase is mainly andesine, but is confined to the northeast quarter, and for the bordering the shore, and pebbles of foreign mate amount. Orthoclase is in all cases very subordinate and inconspicuous. The hornblende is of the common green includes considerable oligoclase. most part to a single great area. The formation rial are therefore rarely found in them. variety. The more basic modifications of this rock consti extends northward a few miles beyond this quad The sandstone of the Swauk formation is gen The pronounced changes, both structural and mineralogi- cal, which the rock has undergone, are seen better under the tute a minor but noticeable proportion of the rangle and eastward across the Mount Stuart quad erally a light-gray arkose, which may be seen microscope than megascopically. The feldspars are partially northern area. 'Locally the granodiorite passes rangle into the valleys of Wenatchee and Columbia megascopically to consist mainly of quartz, feld altered to rather sharply bounded aggregates of secondary into a rock that consists of the same minerals rivers. Its total area is therefore many times that spar, and mica. It is usually distinctly bedded, minerals, which consist mainly of zoisite, with sericitic mica and scapolite. The hornblende is somewhat altered to epi- combined in different proportions, forming a included within the Snoqualmie quadrangle, and and cross-bedding is sometimes visible. The pre dote and chlorite. The effects of dynamic metamorphism quartz-mica-diorite. As compared with granodio it is, in fact, one of the most extensive sedimentary vailing medium-grained sandstone is interstratified are strikingly illustrated in all the slides. The quartz shows very marked strain shadows, and there is much finely rite this rock has less quartz, less orthoclase, and formations in the Cascades. with beds of shale and conglomerate. The shale crushed feldspar, quartz, and hornblende between the larger more of the ferromagnesian constituents, with the Relations. The relation of the Swauk to the is usually rather dark and carbonaceous, and fre grains. This fine interstitial material in some places appears hornblende commonly in excess of the biotite. pre-Tertiary rocks is one of strong unconformity. quently contains well-preserved leaf impressions. to "flow" about large rounded individuals of feldspar, as in a typical "augen" gneiss. In the large plagioclase crystals the From granodiorite to quartz-mica-diorite there This relation is shown not only by the contrast of NACHES FORMATION. twin lamellae are frequently curved and faulted and some of are, naturally, all gradations. In this graded series the metamorphism and high inclination of the older the feldspar shows an extremely minute polysynthetic twin ning, which was probably induced by great pressure. a rock in which the orthoclase is unessential may rocks on the one hand to the relatively slight alter General character and distribution. The Naches be assigned to diorite. A still more pronounced ation and open folding of the Eocene on the other, formation is composed of interbedded sandstone MOUNT STUART GRANODIORITE. departure from the prevailing type is seen near the but by the fact that the basal conglomerates of the and basalt, the sedimentary rock predominating General character and occurrence. This rock is contact with the serpentine on Fortune Creek, Swauk contain bowlders of serpentine and grano in the lower, and the volcanic in the upper por a granular intrusive, light gray in color and resem where the intrusive rock is a quartz-diorite, free diorite, the more recent of the .pre-Tertiary rocks. tion. The formation is named for the river in bling granite in appearance. In the Mount Stuart from biotite, in which the hornblende is pale green. The formation next younger than the Swauk is whose basin it is most extensively developed. quadrangle this granodiorite is very extensively Here it is somewhat foliated. the Teanaway basalt, whkh generally overlies it, The main area, which has a northwest-southeast developed and forms the peak for which the quad Granodiorite of this type prevails in all the south but in the northern part of the quadrangle it is trend, extends along the northeast side of the rangle and the formation are named. In the Sno- ern areas except the one at the head of Little Creek, overlain by the Keechelus, a volcanic formation of Naches basin and continues to Yakima Valley. qualmie quadrangle there are correlated with the where the rock is rather darker and finer grained Miocene age. It is intruded by late Tertiary gran The only other important areas lie just north of type occurrence, on the basis of lithologic character than typical granodiorite, with a notably large odiorite and diorite. the principal one. No occurrences of the Naches and relations, one area near the northeast corner proportion of hornblende. Under the microscope The Eocene age of the formation has been deter formation are known outside of the Snoqualmie and several in the southeast quarter. In all these the rock shows profound alteration, the feldspars mined from fossil leaves. The only known locality quadrangle. areas there are good exposures that clearly show especially being changed to clear mosaics. Biotite in the Snoqualmie quadrangle where these may be Relations and age. The base of the Naches the relations of the granodiorite to the contiguous is an essential constituent, which differentiates this collected is on the ridge between the Middle Fork formation is exposed at only a few places, where, rocks. rock from the quartz-diorite already described. of the Teanaway and Clealum River. In the like the Swauk, it rests directly on highly meta Relations and age. The granodiorite of the mass Relation to quartz-diorite. The grounds, litho Mount Stuart quadrangle they are most abundant morphosed pre-Tertiary rocks with marked uncon from which Mount Stuart is carved is intrusive in logic in character, for separating the Mount Stuart and best preserved in the vicinity of Liberty, on formity. This contact is generally covered, however, all the other pre-Tertiary formations, and is over granodiorite and the quartz-diorite just described Swauk Creek. Dr. F. H. Knowlton has examined by the Kachess rhyolite, a rock that bears a lain by the Eocene. The northern granodiorite may now be concisely indicated. On comparing a collection of leaves from this locality and reports peculiar relation to the Naches and is in part area of the Snoqualmie quadrangle shows the same the dominant types of the two the following impor that they indicate that the Swauk formation is of contemporaneous with it, so that a heavy flow of geologic relations, being clearly intrusive in the tant differences appear. First, in the granodiorite Eocene age. Kachess rhyolite is interbedded with the Naches Hawkins greenstone and in the peridotite, and orthoclase, though subordinate to plagioclase, is an Thickness. The thickness of the Swauk forma sandstone and basalt. The upper surface of the overlain at the eastern base of Goat Mountain by essential constituent, but it is not essential to the tion is widely different in different parts of its Naches formation, where it is not in contact with the Swauk formation, of Eocene age. The relations quartz-diorite. Second, biotite constantly occurs area. Perhaps the best exposure in the Snoqual the Kachess, is overlain unconformably by the of the southern masses, which form a definite group in considerable amount in the granodiorite, and mie quadrangle, and the one showing the greatest Keechelus volcanics. The strata of the Naches and presumably belong to the same epoch of intru even in most of the basic varieties of rock into thickness, is seen on the east and southeast sides have been thrown into open folds and usually sion, define their age less narrowly. They are which it locally passes, but is absent from the of Goat Mountain, whose base is traversed by the dip at angles ranging from 30° to 60°. intrusive in various pre-Tertiary formations, while quartz-diorite. Third, the quartz-diorite is char contact of the Swauk upon the pre-Tertiary rocks Since the Naches and Swauk formations are not Eocene rhyolite and Miocene basalt lie upon the acterized throughout by a secondary foliation, indi and whose summit is formed by Miocene volcanics. found in juxtaposition, there is a lack of direct eroded surfaces of the masses with which they are cating that it has been subjected to enormous The total thickness of the Swauk exposed here is stratigraphic evidence regarding their relative ages. in contact. This relation to the Tertiary rocks pressure, but such foliation is not shown, except over 5000 feet. It is probable, however, that the It is noteworthy, however, that they have similar relations to both, the older and the later rocks, a No conglomerate was seen in the Naches forma Swauk formations were deposited. It continued Unimportant accessories are magnetite, zircon, and fact which suggests that' they may be nearly con tion except at one point on the southwest side of during the later half of the Naches-Swauk epoch apatite. The rock is slightly weathered, the feld temporaneous. The evidence afforded by fossil the ridge of pre-Tertiary rocks in the southeast and for some time after its close, and persisted spars being somewhat clouded with kaolin and seri plants confirms this view. The shales of the quarter, where a thin bed of conglomerate con during the early stages of the eruption of the Tean cite, and limonite occurring in miarolitic cavities. Naches formation have at two localities yielded taining pebbles of slate and quartz separates the away basalt. The eruptions which occurred during Analysis of Kachess rhyolite from near Easton. fossil leaves, which have been examined by Dr. Kachess rhyolite from the Peshastin slate. the deposition of the early Eocene sediments were F. H. Knowlton, who comments upon them^as The basaltic material occurs in three forms confined almost entirely to the Naches basin. SiO...... 76.17 TiO2 ...... :20 follows: intrusive dikes and sheets, massive flows, and Later, the rhyolite flows extended farther north A1S O3 ...... 12.32 ZrO 8 ...... 03 Fe,O,...... 1.47 CO3 ...... none. fragmental beds, or tuffs. Of these three, the ward and covered'the western part of the Swauk The plants .... belong to unpublished species of FeO...... 20 P,QB ...... 04 flows are the most important. beds as well as the Naches to a considerable depth. MgO...... none. SOS ...... none. Juglans and Ficus and are the same as those found at the CaO...... 17 8...... none. locality west of Liberty [in the Mount Stuart quad The basalt of the intrusions and flows is grayish Thickness. The rhyolite shows a maximum Na8 O...... 3.94 NiO ...... none. rangle]; hence, I assume, are to be referred to the black or dark gray on fresh fracture. It exhibits thickness of about 4000 feet, an amount which is Ka O...... 4.27 MriO...... none. Swank. The Species of Juglans is distinct and unmis coarse p'hases, in which the crystalline texture is derived from measurement of sections across the H2 O ...... , .23 BaO...... 10 H,O+...... 79 SrO..... not looked for. takable, and neither this nor the Ficus have before evident, and finer ones which appear aphanitic. main area and which, being the sum of the maxima appeared outside of the Liberty locality. The flows may be generally distinguished by for all the sheets, is greater than the thickness 99.93 Although similar relations and similar fauna their highly vesicular upper surfaces; the rock of actually accumulated at any particular point. The The rock is thus composed essentially of silica, indicate the contemporaneity of the Swauk and the intrusive bodies being, on the contrary, almost rhyolite thins out in some places, however, with alumina, and the alkalies. The considerable Naches formations, evidence now to be stated seems entirely compact, though sometimes slightly vesic striking abruptness, as is illustrated, for example, amount of ferric oxide is probably for the most to justify mapping them as distinct units. Accord ular near the contacts with the sediments. The by the difference' in its thickness on the opposite part combined with water in limonite and may be ing to the hypothesis on which the separation is fragmental volcanics are dark olive-green tuffs, sides of the ridge east of. Kachess Lake, as well as largely of extraneous origin. The essential min- based, the area of pre-Tertiary rocks extending composed of angular, mostly vesicular fragments. by the flow intercalated with the Naches strata, eralogical composition of the rock as calculated southeastward from Easton once formed a divide They are much more decomposed than the massive which thins out abruptly to the west of Quartz from the analysis is as follows: between basins on the north and on the south. basalts, and have a dull, earthy appearance. Their Creek. This pronounced variability in thickness - Mineralogical composition of Kachess rhyolite. In the basin to the north, sediments were deposited green color is due to the presence of abundant iron- is probably due to the viscosity of the lava and not Quartz ...... 35.8 Ilmenite...... 5 without admixture of basaltic material, but in the bearing secondary silicates. to the fact that the rhyolite was poured out upon Orthoclase ...... 25.6 Hematite...... 1.4 area south of this ridge basalt flows were intercal The microscopic petrography of the Naches a very uneven surface or 'that subsequent to its Albite...... 33.6 Water...... r*. 1.0 ated with beds of sand. basalt may be omitted here, since the rock is extrusion it was deeply eroded. The variations in Anorthite...... 1.4 Excess* of ALO. West of the Kachess lakes the Swauk sandstone entirely similar to the Teanaway basalt, which thickness are indicated in the structure sections as * The excess of alumina probably is in the form of kaolin. is overlain by volcanic formations, but in its south- will be discussed in greater detail. definitely as the scale will permit. westernmost exposures the Swauk formation is not Petrography. In addition to the general char According to the quantitative classification, the ably thinner than elsewhere. In a similar way the KACHESS RHYOLITE. acters already noted the details of constitution and rock is a liparose. Naches formation rapidly thins eastward as it General character and occurrence. The Kachess texture of these rhyolites may be further described. The andesite in the areas northwest of Clealum Lake and approaches the area of pre-Tertiary schist. The rhyolite is named for Kachess Lake, on whose Although prevailingly creamy white or gray, they east of Kachess Lake weathers almost white, but on fresh thin bed of sandstone exposed immediately west northeast side it is well exposed. The formation sometimes show pale hues of green, purple, pink, fracture it is light olive or sage green. It is seen megascop- ically to consist mainly of an aphanitic groundmass in which of Easton connects southward with the main body comprises several flows of acidic lava. Through or brown. A delicate banding, due to alternation are embedded, rather sparingly, small phenocrysts of white of Naches sandstone, and this connection is inter out a large part of its extent it is separated by of lighter and darker layers, is common. Their feldspar. Microscopically these feldspars are found to be much altered plagioclase. The rock contains pseudomorphs preted as showing that the two basins may have interbedded sandstones and basalts into several texture is usually stony and in some places com of quartz, chlorite,, and calcite that seem to represent pheno been joined during the later part of the Swauk- distinct rhyolitic sheets, but elsewhere these sheets pletely aphanitic, but generally small phenocrysts crysts of a ferromagnesian mineral. The groundmass has the Naches epoch. Inasmuch as the later formations merge together and, owing to their lithologic simi of feldspar, sometimes accompanied by quartz, are typical andesitic texture and is impregnated with a secondary chloritic mineral. The rock is thus plainly andesitic, but it overlap both the Swauk and Naches on the west, larity, can not be distinguished. They must there visible. Bather exceptional are glassy phases, can hardly be determined more specifically. it is possible that a mile or two farther west the fore be mapped together as one formation. either gray or lustrous coal-black in color. TB ANA WAY BASALT. connection between the basins was made earlier. The Kachess rhyolite has been observed only Spherulitic structures are common, the -spher- However, all that is known regarding the litho- in the Snoqualmie quadrangle, where it is devel ulites being small and inconspicuous in some Occurrence and general character.- The Tean logic character and areal relations of the two for oped mainly within a zone extending from the specimens, but in certain exposures on Quartz away basalt has been fully described in the Mount mations favors the view that they were deposited southeast corner northwestward somewhat beyond Creek attaining a diameter of 2 or 3 inches. Stuart folio. It was named for the river in whose in basins that were separated during the greater Little Kachess Lake. .An isolated area of rhyo Examined microscopically, the rhyolites exhibit basin it is most extensively developed. It extends part of the epoch and that the eruption of basalt lite east of Clealum River is correlated with the a notably constant and simple composition. Their from this river basin westward into the Snoqualmie was confined to the southern basin until the close Kachess, as well as a larger area at the head of essential constituents are sodic plagioclase, quartz, quadrangle, where there are several large areas, of this epoch. Clealum Lake. and orthoclase, accompanied in some cases by glass. chiefly in the central and northern parts, with Thickness. No very accurate estimate of the The formation is composed chiefly of rhyolite, Accessories are magnetite, apatite, and zircon, in some small ones in the southern part. thickness of the Naches formation is possible. which, owing to its hardness and the poor soil it small quantities. Ferromagnesian constituents Although the formation is composed predomi The" maximum is given by a section across the furnishes, is carved into rugged forms that are but are almost completely absent. Considerable nantly of basalt, it comprises also some andesite, 'folded strata north of Bear Creek, which indicates scantily covered with vegetation. The rhyolite is alteration is shown in all the specimens, giving rhyolite, sandstone, and conglomerate. The basalt a thickness of about 4000 feet. Some allowance in general of lighter color than any other rock of rise to kaplin, sericite, and sometimes calcite and and andesite are mainly massive, but partly frag should be made, perhaps, for repetition due to the region, being commonly a creamy white or a little chloritic matter. mental. The massive basalt is dark gray or, in structural details not seen, but, on the other hand, light yellow. It usually has a platy parting, Texturally the majority of specimens are porphyritie and some places, greenish to brownish, hard, and resist some of the Naches formation probably had been which causes it to disintegrate into thin slabs the phenocrysts are mainly of sodic oligoclase or albite. ant to erosion so that it is well exposed and -gives removed by erosion before the Keechelus andesites that form characteristic talus on the steep slopes. Porphyritie quartz is rarely present, and phenocrysts of rise to prominent ridges with steep slopes sparingly orthoclase are not common. The groundmasses, which con covered it. To the northeast the* formation thins Excellent exposures showing these characteristics sist of plagioclase, quartz, and orthoclase, exhibit an inter clothed with vegetation. It generally becomes out rapidly as the principal mass of Easton schist are found in the basins of Quartz Creek and esting variety of textures, of which the leading types are as somewhat reddish on weathered surfaces, and follows: is approached. There is, however, no evidence Little Creek, and an easily accessible one lies just (1) Glassy, Consisting mainly of glass, with various kinds decomposes to a rust-red soil. It is everywhere that the Naches was extensively eroded before the south of the railroad a short distance west of of crystallites. (2) Felsitic. Consisting of minute, irregular much jointed, in some places irregularly, in others overlying Kachess rhyolite was poured out, and, Easton. A thin bed of brick-red, decomposed grains of feldspar and quartz. This texture is frequently so into horizontal plates, but comparatively rarely fine grained that the minerals are not readily distinguished, indeed, the eruption of this lava began well back in rocl?, apparently andesite, is intercalated with the and there may in some., cases be a little glass. (3) Fibrous. into the regular vertical columns so characteristic the period of Naches sedimentation. The thinning, rhyolite in the area between the two forks of Feldspar occurs in minute fibrous crystals which may form of basalt in general. The andesite is of similar aggregates of several kinds as (a) spherulitic, radiating from therefore, probably indicates not greater erosion in Quartz Creek. A thicker bed of andesite consti a point and approximately spherical; (&) longulitic, radiating general appearance but is distinguishable chiefly this vicinity but proximity to the shore line of the tutes the base of the formation west of the head of from a line and approximately ellipsoidal; (c) sheaf-like, form by porphyritie texture, not seen in the basalt. basin in which the formation was deposited. Clealum Lake and is poorly exposed on the east ing bundles of nearly parallel fibers, divergent at the ends; (d) The fragmental rocks are made up of angular confused irregular aggregates. The groundmasses are in 110 Liihology. The Naches formation is composed ern side of Kachess Lake. This rock is of light case composed entirely of fibres, for between the fibrous pieces of lava, consolidated by secondary cemen of interbedded sedimentary and volcanic rocks, the greenish-gray color and is not conspicuously differ aggregates there is always some interstitial matter which tation into masses more or less firm, the coarser may be inicrogranular, vitreous, or micropegrnatitic. Some latter of basaltic character. Its lower portion con ent from the rhyolite. phenocrysts of quartz and feldspar have fibrous borders, of material into agglomerates, and the finer into tuffs. sists principally of sandstone, with which is inter Relations. The relations of the Kachess to other which the main portion extinguishes with the nucleus. (4) The sedimentary rocks, with an exception to be calated a rather subordinate amount of basaltic formations are peculiar. In the southern part of Micropegmqtitic. Composed of intergrown quartz and alkali noted in its place, are arkose sandstones, quite feldspar. With the micropegmatite may be associated micro- material representing contemporaneous extrusions. the quadrangle the Kachess rhyolite forms three granular or fibrous material. (5) Micropoikilitio. Minute distinct in composition from the basalt tuffs. A The basalt, however, becomes increasingly impor main bodies; one interbedded with the Naches for laths of feldspar tying in various directions are inclosed in small amount of rhyolite tuff, petrographically much larger irregular grains of quartz.., . , ; , similar and probably equivalent in age to some of tant in the higher beds, and is dominant in the mation, one between the Naches and the Teanaway The nonporphyritic rhyolites exhibit felsitic, glassy, and uppermost part of the formation. basalt; and one above the southern extension of spherulitic textures, the best development of the last being the upper Kachess rhyolite, occurs locally, but in The sandstone, which is perhaps the most impor the Teanaway basalt. In the northern part there shown in nonporphyritic specimens. Glassy textures are insignificant masses, not large enough to be repre noticeably rare in these rhyolites. Probably part of , the tant member"of the Naches formation, is similar to is one small mass, just south of Howson Creek, rocks were originally glassy but have undergone devitrifi sented on the scale of the map. the typical sandstone of the Swauk. It is rather interbedded with the Swauk, a main body of cation, and;, in some specimens, there are clear indications of The sections 'of the Teanaway basalt differ from such a change. It is probable, however, on the other hand, point to point. No attempt will be made to trace light 'gray, weathering in tawny hues, and the rhyolite between the Swauk and Teanaway, and that much of the material solidified in a holocrystalline con grains, which are not well rounded, are of quartz a little rhyolite, in masses too small to map, locally dition, indicating that it was partly extruded in great flows out these variations in detail, but the general char and feldspar with a subordinate quantity of schis interbedded with the Teanaway basalt. In the which cooled slowly. acter of several exposures will be briefly indicated. tose and slaty material. The rock generally shows southern part of the quadrangle the rhyolite flows The chemical composition of a typical Specimen The northernmost extensive section, at the head of "distinct bedding, and at some places cross-bedding, extend eastward beyond the limits of the Naches is shown in the following analysis by Mr: George Clealum River, shows considerable green indurated although at other localities it is massive and breaks formation and thus lie in places directly upon the Steiger of the United States Geological'Survey. tuff and breccia in its central part, with basalt doWn. in great blocks. 'pre-Tertiary rocks, these relations indicating trans The specimen is white in the portion from, which above and below, interbedded with a little arkose The shales, which are interbedded with the gression by the lava flows beyond the shore line of the material was taken for analysis, but in other sandstone. The sections on either side of Clealum sandstone in rather subordinate quantity, are the Naches basin. parts is much stained with limonite. Microscopi Lake have at the very base a peculiar conglomer olive to brownish black in color, the darker phases The episode of eruptions which the Kachess cally it is seen to bear small phenocrysts of albite ate consisting of pebbles of Kachess rocks embed being carbonaceous. These fine-grained beds have rhyolite represents began at some time near the in a groundmass of quartz and alkali feldspar ded in a matrix composed of ordinary sand and yielded the fossil leaves already described. middle of the epoch in which the Naches and which aije mostly in micropegmatitic intergrowth. basaltic tuff, and this rock is overlain by several Snoqualmie. 6 hundred feet of tuff. The tuffs on the eastern side times with a tinge of violet indicating that it reverse is true, and the position of a dike is in which the Boslyn sandstone was deposited; of the valley are green and red, while those on the contains titanium. The accessories are abundant marked by a notch in the crest line. The pro The conclusions formed from the study of the western side are green. Above the tuffs lie several magnetite and some apatite. In addition to these jecting dikes are being reduced mainly by mechan flora are in accord with the stratigraphic rela thousand feet of rocks that are nearly all lava. minerals, which are invariably present, the rock ical disintegration and break down into angular tions already noted. The unconformity between An excellent and characteristic exposure of the may contain a little hypersthene. Olivine has rubble which spreads over the sandstone. There the Swauk formation and the Teanaway basalt upper part of the great body of the formation not been found in the specimens of Teanaway fore in places where the dikes are most crowded indicates a time interval, while the eruption of the appears on the face of Easton Mountain, and this basalt from this quadrangle, but its original pres the intervening sedimentary rock is completely basaltic lavas over this region furnishes a further section consists chiefly of lava. The mass inter- ence in much of the rock is shown by pseu- covered with basalt fragments, so that a general cause for the nonsurvival of species belonging to bedded with the Kachess rhyolite south of Yakima domorphs of characteristic outline. Glass is view of a large area might lead to the conclusion the Swauk flora and for their absence from the Valley is all basalt. The section along Guye commonly present, in some specimens in consid that the underlying rock there was all basalt. Roslyn flora. Creek contains several beds of leaf-bearing shale erable amount, and in many specimens where no The tracing of these dikes is often difficult and Lithology. The greater part of the Roslyn and sandstone. This carbonaceous rock has been glass is found there are indications that it was their representation on the map is necessarily formation consists of massive sandstone, rather prospected for coal, but these beds represent simply originally present but has undergone devitrification inadequate. The dikes are generally well exposed more yellowish in color than the typical Swauk lenses of sandy mud, of very limited extent, that or replacement. on ridge tops and can there be mapped completely, sandstone. With the sandstone occur fine-grained were deposited in depressions in lava sheets and but many dikes seen on the crests can not be clay shales and coarser arenaceous phases. The covered by the later flows. The textures of the basalts are varied,, the most common traced down the slopes because they are there stratification of the sandstone is not strongly being the intersertal. Typical ophitic texture has not been Relations and age. The Eocene age of the Tean- notecj, although the augite often incloses the plagioclase, covered by waste. This explains why so many marked as a rule, and irregularities of bedding away basalt is at once shown by the fact that it is which occurs in lath-shaped crystals or microlites. Fluidal more dikes are mapped on the crests than on the and local unconformities can be seen at some arrangement of the feldspar laths is seen in some specimens. underlain by the Swauk and overlain by the Ros- A decidedly porphyritic structure is not common, but in some slopes. Again, in the area where the dikes are localities. Conglomeratic beds are not common, lyn, sedimentary formations that bear Eocene flora. specimens there are phenocrysts of feldspar, augite, and most abundant, the task of tracing them is made pebble bands in the sandstone being the coarsest The relations of the basalt to the rocks beneath olivine. extremely difficult by the merging of the debris material usually found. Although the Roslyn An exceptional phase is a quartz-basalt found near the show that its outpouring was immediately pre head of the West Fork of Clealum River. This rock con from contiguous dikes, and even where all the dikes formation appears to overlie conformably the ceded by a period of general erosion. Evidence of tains a few phenocrysts of plagioclase and augite, with possi are traceable they can not all be represented, on Teanaway basalt, the basal sediments are dis bly some of olivine (replaced by chlorite or serpentine), and this is afforded in the Mount Stuart quadrangle by corroded grains of quartz surrounded, as in most quartz- the scale of the map. In this area, then, only the tinct in essential composition from the basaltic the unevenness of the surface of the underlying basalts, by wreaths of glass and augite. A similar rock larger and better-exposed dikes are mapped. tuffs. The sandstone occurring near the base Swauk sandstone. In the Snoqualmie quadrangle occurs in this formation in the eastern part of the Mount Petrography. Petrogra pineal ly, these dike rocks is a siliceous arkose but is often darker than Stuart quadrangle. the unconformity at the base of the Teanaway may The Teanaway basalt in general shows much alteration. show a distinct relationship to the Teanaway basalt. higher beds, by reason, possibly, of slight admix be most plainly observed at a point northwest of Of all the minerals, the feldspars show the least decomposi In texture they are are generally holocrystalline ture of material derived from the basalt series. tion, but are generally somewhat altered, giving rise to Clealum Lake, where the formation overlaps the kaolin, sericitie mica, and at some places scapolite and and either porphyritic or typically diabasic. The .The portion of the formation containing coal beveled edge of the Kachess rhyolite, from which zoisite. The ferromagnesian minerals are attacked in differ texture is usually coarser in the wider dikes, but beds will be described more particularly under it is separated by a tuff-conglomerate containing ent degrees. While the olivine has entirely disappeared, and sometimes other factors enter, so that no constant the heading "Economic geology." the hypersthene when present is more or less altered, the pebbles of the rhyolite. As the time interval augite is often perfectly fresh. The most abundant and most relation exists between the texture and the width between the Swauk and the Teanaway was suffi characteristic secondary product derived from the ferromag of the dike. The porphyritic rocks, which are of MANASTASH FORMATION. nesian minerals is a serpentinoid substance of deep olive-green cient not only for this extensive erosion but also or reddish-brown color and high double refraction, which subordinate importance, contain abundant pheno Occurrence and relations. The youngest of the for the outpouring of much of the Kachess rhyo appears to be iddingsite. Other secondary minerals occur crysts of plagioclase and pyroxene and might be Eocene sedimentary formations occurs on the lite, it must have been very considerable. On the ring in the basalt are calcite, uralitic hornblende, epidote, classified either as basic augite-andesite-porphyries headwaters of Manasta&h Creek, for which it is chlorite, and serpentine. other hand, there is no evidence of a long interval or as diabase-porphyries. named, and on Taneum Creek. At most places between the Teanaway and the overlying Roslyn Analysis of a typical specimen of the Teanaway Microscopically, the plagioclase crystals are found to be where it is seen the Manastash sandstone rests sandstone. basalt given in folio 106 shows that it belongs, mainly labradorite, but they generally show zonal structure directly upon the Easton schist, and at some Additional evidence regarding the age of the and have rims that are more sodic in composition. The places it is accompanied by a well-developed according to the quantitative classification, to pyroxene is chiefly augite, with which hypersthene is in basalt is given by remnants of plants collected on vaalose. places intergrown; in rare instances the rhombic pyroxene is basal conglomerate. On both forks of Taneum Gale Creek from a bed of sandstone intercalated The andesites occurring as flows intercalated more abundant than the monoclinic. In the porphyries the Creek the sandstone is exposed beneath the Yak groundinasses are of plagioclase and pyroxene, often with with the lava flows, and this flora is valuable chiefly with the basalt sheets belong to the pyroxene- ophitic texture. In the ophitic diabases the chief constit ima basalt and the Taneum andesite, both of as suggesting correlations with formations on the bearing varieties. Megascopically they are por uents are labradorite and augite. Both hypersthene and Miocene age, and in the more northern of these west side of the Cascades. These plant remains phyritic rocks showing phenocrysts of feldspar olivine may occur in them, together or separately. Greenish- two occurrences, the sandstone rests upon the brown hornblende, apparently original, is here and there have been submitted to Dr. Kiiowlton, who has and less conspicuous ones of pyroxene in a dark present in small amounts. Quartz is an essential constituent quartz-diorite. In all of these small areas the reported upon them as follows: greenish-gray to black, fine-grained ground mass. of a large proportion of the specimens, including many of Manastash sandstone is poorly exposed, so that those that contain olivine. It forms anhedra and is gen the knowledge of the formation has been gained This is a collection consisting of a dozen or more pieces Under the microscope the feldspar phenocrysts are seen to erally intergrown with orthoclase in interstitial masses of of matrix showing numerous impressions. I note the fol be chiefly labradorite. The phenocrysts of pyroxene include micropegmatite. These basic dike rocks are considerably chiefly in the larger area farther .east, in the altered, but to a less extent than the surface lavas of the lowing genera: Populus sp., Ficus sp.; Plerospermltes sp., augite and hypersthene, the augite generally fresh, but the Mount Stuart quadrangle. hypersthene largely or even completely replaced by the olive- same age. Their most characteristic secondary constituent Ulmus (f) sp. green tq reddish micaceous material to which hypersthene is iddingsite or a related mineral, which is derived both from Lithology. The Manastash, like the other I do not recognize any of the species in this collection. so frequently alters, The groundmass contains a second gen olivine and froni hypersthene. Eocene sedimentary formations, comprises sand A chemical analysis of a typical basic dike roc.k from the The genera are sufficiently clear, but the species are new eration of plagioclase and the pyroxenes, together with a stones and shales. East of Frost Mountain, a and are unlike any heretofore obtained. The forms are little finely granular paste, apparently of quartz and feld North Fork of Teanaway River has been published in the Mount Stuart folio. The rock is a quartz-bearing olivine peak in the Mount Stuart quadrangle, between not similar to those found in either the Eoslyn or the spar, and a good deal of the secondary mineral already men tioned, in a finely divided state. A little glass is in some diabase containing some hornblende. It is more siliceous the south forks of Taneum and Manastash creeks, Swauk, but appear to find their greatest affinity with places present. The usual accessories, magnetite and apa than the Teanaway basalt analyzed, and according to the material from the west side of the Cascades, at Car tite, occur. quantitative system it is classified as tonalose. Notwith the sandstones are well exposed and are massive bonado and vicinity. For example, no Eocene species standing this difference, however, the basalt and diabase and quartzose with pebble bands, white quartz BASIC DIKES AND SHEETS. show marked mineralogical and chemical relationship. of Populus has heretofore been found east of the Cascades, being most abundant among the pebbles. The while several forms have been found about Carbonado, Occurrence. The Swauk sandstone and the older Rosi/risr FORMATION. shale is fine grained and in the Mount Stuart South Prairie Creek, and Franklin. The species of quadrangle is associated with seams of bone and Ulmus is similar to elm leaves from vein 12 at Franklin, rocks are cut by a great number of basic dikes of Occurrence and general character. The Roslyn but I am not certain that it is absolutely identical. dark, reddish-weathering rock closely resembling formation consists of sandstone and shale and con impure coal. No coaly beds were seen within the the Teanaway basalt. These dikes extend upward tains workable seams of coal which will be described Snoqualmie quadrangle, although the lower area Thickness. The section that would seem to give to the Teanaway basalt and in some favorable local under the heading "Economic geology." Its dis of the Manastash formation on North Fork of most nearly the maximum original thickness of the ities can actually be seen to connect with the lower tribution, so far as known, is restricted to a single Taneum Creek is the western extension of the Teanaway basalt is the one along the ridge east lava flows of that formation. They evidently rep basin, lying chiefly in the Mount Stuart quad sandstone in which a coal seam has been pros of Clealum Lake, where the thickness exposed resent the conduits through which the lava reached rangle. The two rather small areas in the Sno pected at a point in the Mount Stuart quadrangle between the Swauk and Roslyn formations -is the surface, and show plainly that the Teanaway qualmie quadrangle form the westernmost part of about 2 miles east of its western boundary. The about 6000 feet. On the northern border of the basalt was erupted through many fissures rather this basin. small area north of B. M. 5695 contains some quadrangle there is a section of Teanaway rocks, than from a great crater. They are most abundant The formation affords numerous exposures, none reddish, decomposed andesitic tuff. dipping almost vertically, which measures about northeast and northwest of the head of Clealum of them very extensive or conspicuous, since the Age. The age of the Manastash formation has the same. In the southern part of the quadrangle Lake, being thus, in the Snoqualmie as in the rocks composing it are soft and generally become been determined chiefly from a small collection the Teanaway basalt interbedded with the Kachess Mount Stuart quadrangle, mainly confined to the covered with soil. Good sections of parts of it are of fossil plants obtained near the head of North rhyolite is only about 500 feet thick. These belt of Swauk sandstone just beneath the main exposed in the coal mines. The name of the for Fork of Manastash Creek, which indicate that it figures show that the basalt had its maximum body of Teanaway basalt. In a part of the Tean mation is that of the principal coal mine developed is upper Eocene, probably later than the Roslyn. development im the northern areas and was rela away basin they are almost incredibly numerous, in it and is also the name of a mining town situ MIOCENE SERIES. tively thin in its southern extension. and over considerable areas actually occupy more ated immediately east of this quadrangle. The Petrography. Of the rocks constituting the of the surface than the sedimentary rock which thickness of the Eoslyn formation at a locality just The Miocene rocks of the Snoqualmie quad Teanaway formation it seems necessary to give they intrude. east of the quadrangle, where it reaches its maxi rangle are nearly all included in one great area, further description of only the dominant lava The great majority of the dikes form a definite mum, is approximately 3500 feet. which occupies most of the western half and the basalt -and the less important andesite. system, with a trend a little north of east. The Relations and age. The Roslyn formation is extends to the southeastern corner. They are The basalts are mostly dark gray to black on dip is almost constantly steep to the west. In found in contact only with Quaternary deposits almost entirely igneous and mostly volcanic, fresh fracture, usually with a tinge of green. Gen addition to the nearly vertical dikes there are a and the Teanaway basalt. It overlies the basalt including the Taneum andesite, the Guye for erally they are fine and even grained, but with few sheets injected between strata, of which only without observed angular unconformity or dis mation (sediments with some basalt and rhyolite), crystalline texture more or less developed. Occa one, which is situated east of Clealum River above tinct evidence of an erosion interval. the Yakima basalt and associated diabase, the sionally, however, there occurs a little pitch-black the lake, is large enough to be mapped. In width The Eocene age of the Roslyn formation has Keechelus volcanic series (mainly andesitic), the glass, which is sometimes so etched on the weath the dikes vary from a few hundred feet to a few been determined by Dr. F. H. Knowlton from pyroxene-diorite associated with this series, the ered surface as to show the existence of alternating inches. They influence the details of relief con collections of fossil plants made at the Roslyn Ellensburg formation (composed of volcanic sed layers more or less susceptible to decomposition. siderably, especially on ridge tops, for on slopes mine, just east of the edge of this quadrangle. iments), and the intrusive Snoqualmie granodio- Microscopic study shows that the chief constitu the mantle of waste obscures the effects of differ The Roslyn and Swauk floras have no species in rite. The order in which these formations have ent of the massive basalt is plagioclase, mainly ential erosion. In a great majority of cases the common, which is believed to indicate that the been mentioned is thought to be approximately labradorite. Augite is second in abundance; its dikes weather out more prominently than the plants that grew .while the Swauk sandstones that of age, but our knowledge of their succes color in thin section is generally pale brown, some sandstone on either side, but occasionally the were accumulating did not survive to the time sion is incomplete. The Guye formation is not 7
found in contact with the other Miocene sedi Relations and age. The Guye formation has The conglomerate exposed near Snoqualmie ceded by an erosion period. The southern masses mentary formation, and the paleontological evi been found in contact only with two later ones. Pass and on Guye Creek is made up of angular have not their bases exposed, but, like the basalt dence upon which it is determined as Miocene The Snoqualmie granodiorite is intrusive in it, and to subangular fragments, mostly of black chert of the Ellensburg quadrangle, are overlain .by the does not fix its age precisely. The Keechelus the Keechelus andesitic series overlies it with or indurated slate much veined with quartz. Ellensburg formation, although the Keechelus series includes some very fresh lavas that may marked unconformity. Associated with these are pebbles of vein quartz. andesite usually intervenes. be of Pliocene or possibly Quaternary age. The The intrusive relation of the granodiorite is The material of this general composition varies Lithology. The Yakima basalt comprises mass Snoqualmie granodiorite is intrusive in and there clearly shown at several localities, perhaps best in grain from conglomerate or breccia, with frag ive lava and fragmental rocks, the lava greatly fore younger than the Guye strata, but no other at the head of Snow Creek, where the contact of ments 2 or 3 inches in diameter, to fine grit. It preponderating. It is well exposed along the high precise data have been obtained regarding its age. the two formations is well exposed. Here the is extremely characteristic of the Guye formation, ridge in the extreme southeast corner of the quad Guye rocks are penetrated by apophyses of the and glacial erratics of the conglomerate, found rangle, where its characteristic features are well TANI5UM ANDESITE. granodiorite, which contains angular inclusions of many miles down the Yakima Valley, are easily displayed, especially in certain landslide areas Occurrence and relations. In the southeastern the rocks invaded. recognizable, since no similar rock occurs in any where the rock may be seen in fresh escarpments. portion of the quadrangle, in the drainage basins The strong unconformity separating the Guye other formation of this region. The massive basalt is nearly black and is generally of Taneum Creek and Little Creek, several square from the Keechelus is shown both on the ridge The chert is light gray in color and is dis much jointed. The prevailing type of jointing is miles of andesitic rocks are exposed. These lie between Denny and Guye creeks and at a point tinctly bedded in layers a few inches thick. It the columnar, but nowhere in the Snoqualmie stratigraphically between the Manastash sandstone southeast of Silver Peak. At both these localities is minutely fissured and veined with quartz. quadrangle are the columns of very regular form. and the Yakima basalt, and are, therefore, probably the Keechelus strata, dipping very gently, form The limestone found at the Guye prospect is Usually the basalt is divided into rudely prismatic of early Miocene age. To distinguish them from the summits and upper slopes, while lower down a light-gray crystalline rock, somewhat marble- masses, standing nearly vertical and cut across by other andesites in this region that are of similar the Guye is exposed with dips near 60°. The like in character. horizontal joints at irregular intervals. Less fre composition but different age, these rocks have actual contacts, unfortunately, are obscured by The rhyolites in "the Guye formation are in the quently there is no conspicuous vertical jointing, been called the Taneum andesite, from the creek talus. main very similar to the Kachess rhyolite, already but only the nearly horizontal platy parting. in whose basin they are chiefly found. This vol The age of the formation is determined by a described. They are light colored and without fer These characteristic partings were produced by canic formation has only a very local occurrence. small collection of fossil leaves which have been romagnesian constituents, but carry quartz pheno the contraction of the basalt on cooling. The It occupies a small area in the Mount Stuart quad examined by Dr. F. H. Knowlton, and reported crysts rather more frequently than the Kachess crevicing of the rock determines the manner of rangle, but is not known outside this immediate upon as follows: rhyolite. A very peculiar apparently rhyolitic its disintegration, and it breaks down into very vicinity. Some of the best exposures of the for rock is found on the southwest shoulder of Ken angular fragments that accumulate as talus at the mation occur along the south side of the North Platanus dissecta Lesq. dall Peak. It consists mainly of a rather hard, base of steep slopes. Fork of Taneum Creek. On Frost Mountain the Acer cequidentatum Lesq. aphanitic groundmass, dull coal-black in color, Ficus n. sp., cf. F. artocarpoides Lesq. Examined in natural exposures or hand specimens, the lava is less than 300 feet thick, but in the Taneum which contains abundant small angular grains and basalt usually appears somewhat crystalline, but is so fine Cinnamomum n. sp. grained that the constituent minerals can not be identified basin it may measure several times that thickness. The first two species are without question Miocene. crystals of quartz. Its texture and composition, megascopically. By microscopic examination, it is found Lithology. The Taneum andesite comprises tuffs The Ficus approaches quite clearly F. artocarpoides, studied microscopically, indicate that it is tuffa- that it is all normal feldspar basalt. The chief constitu and tuff-breccias as well as lavas. These rocks vary which is from the Fort Union group (Eocene) of Mon ceous. Its black color is due partly to an abun ents are plagioclase and atigite. Olivine is usually present, although in very variable amount, and there is nearly always greatly in megascopic appearance. The lavas in tana. The specimen is not perfect and can not there dance of finely divided scaly material resembling fore be positively determined. If it differs at all from some glassy base. Accessories are apatite and magnetite, the main area are generally rather light colored, green biotite and numerous black opaque particles the latter frequently being so abundant that it almost the Fort Union species the difference must be very of undetermined character. deserves to be ranked as an essential constituent. exhibiting shades of gray, brown, pink, and green, slight. Yet the species may prove to be new. The plagioclase forms lath-shaped crystals and shows more and are in large part rough textured and porous. The Cinnamomum is undoubtedly new and is a fine The basalt included in the Guye formation near regular crystallographic development than any of the other The small mass north of the Manastash drainage characteristic species. It does not approach any Kendall Peak is mostly a greenish black, compact, constituents. It is nearly all labradorite and exhibits little zonal structure. The augite, which may form stout prisms or area is a compact, dark-green rock showing a few described species very closely, yet appears to be of aphanitic rock, not very readily distinguished from irregular grains, is generally pale brown, often with a tinge phenocrysts of feldspar, and is not very readily a Tertiary type. the indurated black shale. Its true character was of purple. The olivine forms crystals or rounded grains. It distinguished from the overlying basalt. A very The two species that can be determined are Miocene first recognized by the finding of amygdaloidal is always subordinate in amount to the augite, and in some and the other two are of Tertiary, probably Miocene, specimens is altogether lacking. little rhyolitic material is also associated with the facies. phases, with cavities full of quartz, hornblende, The texture of the basalts is more variable than their com- andesite. and other secondary minerals. A little indurated positio'n. They are hardly ever truly porphyritic, their typi cal texture being the intersertal. All degrees of crystallinity tuff was also found. The microscopic study of By microscopic examination it is found that notwithstand Thus the age of the Guye formation is fixed as are to be observed. Holocrystalline phases occur in which ing its variable appearance, most of the rock of this forma Miocene. Stratigraphic evidence shows that it these rocks demonstrates that they are basalts, the fabric is generally ophitic, and the rapidly cooled upper tion belongs to the single species hypersthene-andesite. The belongs in the early part of that epoch, for it resembling in original constitution the Teana- and lower surfaces of the flows often contain a large propor phenocrysts are of zoned plagioclase and a somewhat decom tion of glass. Generally, however, crystalline matter forms posed ferromagnesian mineral, which in some slides has been is overlain, with marked unconformity, by thou way basalts, already described. Their original the greater portion of the rock. entirely replaced. The plagioclase is mostly sodic labradoi'ite. sands of feet of the Keechelus volcanics, which are nature is masked, however, by changes clue to A chemical analysis has been published in the Mount Stuart folio of a representative specimen from that quadrangle. The principal original ferromagnesian constituent is hyper- the action of the Snoqualmie granodiorite. sthene. When this is present, it is always partly altered to a in turn overlain by the Ellensburg sandstone, of The rock is less basic than typical basalts. It shows close lamellar mineral of high double refraction, which seems to known Miocene age. Yet the stratigraphic rela chemical relationship to the Teanaway basalt, and according YAKIMA BASALT. be iddingsite. In many specimens the original ferromagne tions to the overlying rocks, added to the lithologic to the quantitative classification belongs in the same sub- sian mineral is not found, but is represented by iddingsite rang, vaalose. pseudomorphs with the characteristic forms of hypersthene. resemblance of the Guye formation (composed of Distribution and general character. In Wash interbedded sediments, basalt, and rhyolite) to ington, Oregon, and Idaho a vast area, probably DIABASE. GUYE. FORMATION. the Eocene formations, would have led to its more than 200,000 square miles, is underlain by Occurrence. In the southeastern corner of the General character and occurrence. The Guye reference to the Eocene were it not for the paleo- basalt. The larger part of this great accumula Snoqualmie quadrangle there are several small, formation consists of detrital rocks with some botanic evidence just cited. tion, in the sections where it is best known, is of irregular masses and dikes of diabase which, like chert and limestone and interbedded basalts and Lithology. The Guye formation presents an Miocene age. In the Mount Stuart and Ellens- similar intrusive bodies in the Mount Stuart quad rhyolites. It occurs, so far as is known, only in interesting variety of lithologic types, both sedi burg quadrangles this Miocene basalt forms a per rangle, have been correlated with the Yakima, the northwest quarter of the Snoqualmie quadran mentary and volcanic, and of these the sediments fectly definite unit, which is called, from its basalt. This diabase is a dark-brownish to gray gle, where it is rather extensively exposed. The will be described first. excellent exposures along the Yakima Biver, the ish-black rock, distinguished lithologically from formation is much folded, and its structure can not The shaly rocks, which contain fossil leaves, Yakima basalt. That the Yakima basalt is coex the extrusive basalt by its coarser grain and its be worked out in detail, nor can any general sec are probably the most abundant. They are tensive with the great expanse first mentioned is lack of amygdaloidal structure. It is resistant, tion of it be compiled. Its base is nowhere exposed, partly grayish green and partly black and carbo not certain -but is probable, and if this is so it is and the masses stand in relief above the sur and its top has been removed by erosion, so that naceous. In the southernmost area the fine sedi undoubtedly the most widely distributed volcanic rounding sandstones and basalts. A very prom its limits and its thickness are unknown. The ment has the ordinary aspect of shale, being formation on this continent. inent feature carved from this rock is a crag on general character of the formation may be indi rather soft and fissile. In places these shales In the southern part of the Snoqualmie quad the south side of the Taneum basin, marked with cated, however, by brief descriptions of its princi are somewhat carbonaceous and have been pros rangle, a few small remnants of the western por nearly vertical parallel bands about a foot wide, pal exposures. pected for coal. In areas farther north the shale tion of this great basalt sheet occur. They are slightly darker or lighter according to their min The southernmost occurrence of the Guye forma is. commonly harder, more compact, and much mainly of black, compact lava, with hardly any of eral composition. The crag and its peculiar band tion lies northwest of the head of Lake Keechelus. more resistant to erosion, and breaks under the the fragmental material that forms a considerable ing are visible for many miles. On the creek draining Silver Peak are rather poor hammer with conchoidal fracture rather than part of the formation as exposed in the Ellensburg The diabase is found in irruptive contact with exposures of dark shale and gray sandstone dip along bedding planes, resembling slate in its quadrangle. the pre-Tertiary rocks the Taneum andesite, the ping to the north. Upon these sedimentary rocks induration but differing from it in being free One of the best exposures of the Yakima basalt Manastash sandstone, and the Yakima basalt. rests a great thickness of light-colored rhyolite, from secondary cleavage. The induration is in the Snoqualmie quadrangle may be seen at the Since no extrusive basalts later than the Yakima indicated on the map. In the vicinity of Sno probably due to the intrusion of the Snoqual head of Quartz Creek, where a great landslide has are known in the vicinity of these occurrences, qualmie Pass there are exposures of shale and mie granodiorite, the nature of whose action will produced an escarpment of the black rock over these relations of the diabase observed in both sandstone mingled with prominent beds of con be discussed further on. looking a broad expanse of crumbling hummocks the Snoqualmie and Mount Stuart quadrangles glomerate. Kendall Peak is carved from steeply The sandstone contains rock fragments and and loose angular rubble. The tendency to form as well as its petrographic character, indicate that inclined beds of Guye rocks, its sharp spurs and approaches an arkose. Its grains comprise, in cliff and talus is characteristic, owing to the readi it originated from the same magma as the Yakima pinnacles being formed of the harder beds. In addition to quartz, much feldspar and some mica. ness with which the rock is broken down in large basalt and represents in part the reservoirs or con this vicinity the formation is represented chiefly In color it varies according to composition from fragments, combined with its slowness in disinte duits from which the Miocene lavas were extruded. by sandstones, with some shale, and interbedded light gray or olive to dark grayish or purplish gration. It decomposes to a rust-red soil, which in The question arises here whether the irregular with these are considerable basalt and a little rhy brown. Like the shale, the sandstone exhibits this area is generally very thin. masses represent underground chambers from olite, both occurring in massive and in fragmental various degrees of induration. At considerable Relations. The correlation of the largest areas which the basalt escaped to the surface through form. Commonwealth and Guye creeks also afford distances from the granodiorite it is but moder of the basalt here described with the Yakima basalt fissures, or chimney-like vents which themselves good exposures, which show mainly greenish-gray ately hard and somewhat porous, but in the is made confidently, since they are practically con extended to the surface. Evidence on this point to blue-gray indurated shales, with some rather exposures on Kendall Peak it is closely cemented, tinuous with the type areas of the formation. The is to be looked for in the character of the adjacent coarse grit. Near Chair Peak there is exposed a taking on the character of tough quartzite, and rock of the other areas is similar and agrees in rela volcanic deposits. Lavas may emanate from cra considerable mass of chert, with rhyolite in too breaks with conchoidal fracture. Some of the tions, so far as those are known, with the typical ters or from fissures, and some of the greatest lava small amount for mapping. At the Guye iron lighter arkose phases resemble fine-grained gran Yakima basalt. The rock of the northern areas floods, such as those of the Columbia Plain, are prospect the formation includes one or two beds ite. On microscopic examination it is found that overlies various formations, ranging from the known to have originated by fissure eruption. It of limestone whose aggregate thickness is only a the cement is composed essentially of quartz and Easton schist to the Taneum andesite, in such is a generally accepted belief on the other hand few feet. sericite. a way as to indicate that its eruption was pre that tuffs, which represent explosive eruptions, Snoqualmie. 8 are usually erupted from craters. If these irreg lite, the largest observed in the Keechelus series, extinct volcanoes of the Cascade Range, and in the The original petrographic characters of the ular diabase masses are volcanic necks, we should forms a hill southeast of Pyramid Peak. About vicinity of Arch Rock there are great volumes of pyroxeue-andesites are well illustrated by a expect to find accumulations of tuff in their vicin Green Pass the rocks are chiefly the characteristic yellow fresh-looking tuff. The difference in alter specimen collected from the Naches Valley, near ity. Although no considerable masses of basaltic green andesitic tuffs, with some lighter colored ation between the older and the younger lavas is B. M. 3119. It is perfectly fresh, and therefore tuff occur in this immediate neighborhood, there ones, some dark-gray and pinkish andesite, and made still more evident by microscopic study. probably belongs to one of the later post-Miocene are included in the Yakima basalt series as exposed considerable basalt. Many cuts along the North As regards structure, the older portion has been flows. Megascopically it shows abundant pheno near the northwest corner of the Ellensburg quad ern Pacific Railway afford good exposures of somewhat tilted and gently folded, as shown in the crysts of glassy striated feldspar, and less numerous rangle, at a point about 5 miles distant from the Keechelus rocks, here chiefly red and green structure sections, while the younger rocks display ones of black pyroxene, which are not prominent diabase areas, several hundred feet of such mate andesitic tuffs, with some basaltic and andesitic only such gentle dips as might be considered the in the black, dense aphanitic groundmass. rial, the greatest thickness thus far found in this lava, which is partly dacite. A few miles east initial slope of the lava flows. Microscopically the rock shows the character of a typi formation. The presence of these tuffs would of Martin there is a gully eroded in shales and The topographic evidence is clear in the area cal pyroxene-andesite. The phenocrysts are, in order of naturally lead one to look for traces of volcanic sandstones which form a lens in the Keechelus about Naches Pass, and, although more striking in abundance, labradorite, hypersthene, and augite; the two pyroxenes are frequently intergrown. The groundmass is vents which had been opened through the older series several hundred feet thick but of limited the field, may also be made out by inspection of hyalopilitic, containing plagioclase and both the pyrox rocks. Therefore the occurrence of these diabase horizontal extent. Accounts of the cutting of the the map. The summit of the ridge here is broad enes, of a second generation, embedded in an abundant masses and of heavy layers of tuff within a few Stampede tunnel record the presence of both hard and flat, in contrast with the rugged topography to brown glassy base. As accessories, there occur much mag netite and some apatite. The chemical character of the rock miles of each other supports the hypothesis that lava and shale-like rock, the swelling of which the north, and has every appearance of being near is shown by the following analysis, made by Mr. George the diabase masses represent the roots of basalt upon exposure necessitated a masonry lining. the original surface of the flow and but slightly Steiger of the TJ. S. Geological Survey: volcanoes, and that the absence of tuffs in imme North of Yakima Valley the exposures of this modified by erosion. The lava forming this ridge Analysis of Keechelus hypersthene-andesite. diate proximity to the diabase may be explained formation are on the whole even better than to the appears to have been poured out after the exten SiO...... 62.77 TiO 3 ...... 79 as the result of erosion. south. The eastern shore of Lake Keechelus is in sive erosion which the Cascade Mountains suffered ALO, ...... 14.96 ZrO 9 ...... 03 Petrography. The typical Miocene diabase is a part a steep bluff of hard dark-green dacite-breccia, in Pliocene time. At other localities, however, lava Fe8 O ...... 1.62 CO S ...... none. FeO...... 4.36 P S O 5 ...... 22 dark-brown or gray crystalline rock of medium in which the road could be cut only by blasting. showing a plateau-like upper surface is believed for MgO ...... 1.48 SO 3 ...... none. grain. It has an ophitic texture, best seen on West and north of this lake there are many high other reasons to belong to the older portion of the CaO...... 3.90 S...... none...... 4.31 NiO...... none. weathered surfaces, where the dull-white lath- and rugged peaks carved from Keechelus lavas and series. The only stratigraphic evidence available K 2 0...... 2.13 MnO...... 10 shaped feldspars are contrasted with the dark tuff-breccias, the latter predominating. The lavas is afforded by a locality on the ridge north of H 2 0-...... 51 BaO...... 10 interstitial ferromagnesian material. In a typi are mostly porphyritic pyroxene-andesites and Crow Creek, where a little andesite apparently H 2 O+...... 2.49 SrO ."...... none. cal specimen of fresh rock from the Taneum dacites of different shades of gray, but sometimes overlies the Ellensburg sandstone, but the contact 1.77 basin this texture is illustrated in an even more drab or olive green. In this region there are also is not well enough exposed to prove this relation. The rock contains an unexpectedly high percentage of silica, striking manner. By turning the specimen about small areas of greenish-black basalt and cream- The conditions above described convinced the and the analysis as a whole bears a strong resemblance to that of the Tertiary granodiorite, to be described later, but the in a good light, reflections from the cleavage faces white rhyolite, the rhyolite appearing on the ridge authors that the area mapped as Keechelus com andesite is more siliceous. According to the new quantitative of the pyroxene may be observed, and the rock is south of Alta Mountain. The fragmental rocks of prises lavas of two distinct ages. The two divi classification, it falls in the same division, tonalose. It is evi then seen to be composed of interlocking grains of the northern exposures are chiefly andesitic tuffs and sions in their typical development, the younger as dent that the glass is rich in silica and potash, and that, if it were completely crystallized, it would contain much quartz pyroxene, about 1 centimeter in average diameter, breccias which have in large part been indurated illustrated by the tuffs of Arch Rock and the lavas and considerable orthoclase, both of which are essential con with abundant inclosed lath-shaped feldspars and by the action of secondary agencies, so that they just south of Naches Pass, and the older as illus stituents of the granodiorite. It is clear that this analysis grains of olivine, inconspicuous because of their does not represent the average composition of the Keechelus are as compact and hard as the massive lavas. trated by the lava of Pyramid Peak and the tuffs andesites, many specimens of which, though nearly holocrys- freshness and transparency. Small cavities into The most common of these rocks is a gray breccia, along the ridge to the north, could hardly be con talline, contain little quartz and orthoclase. which the crystals project may be seen in some rather dark on fresh fracture but lighter colored on fused. Along the north side of Greenwater Valley, The other fresh specimens of andesite resemble this speci men more or less closely. The feldspars are zoned and are specimens of the diabase, .and an exceptionally the weathered surfaces, in which the internal struc the boundary between the older and the younger chiefly labradorite. The pyroxenes vary in relative amount, coarse gabbroitic phase occurs at one place in the ture, obscure in unweathered rock, is revealed by rocks could be traced with passable accuracy. In the predominant species being in some cases augite, in others largest area. hypersthene. The groundmass is in some places almost holo- etching. In their larger exposures the tuffs and areas farther south, however, the separation was crystalline and is there composed chiefly of well-formed pritms In microscopic sections these rocks are all seen to have lavas display distinct bedding, and some of the found to be impracticable. Some black andesite of feldspar and of pyroxene in grains or prisms, which gener plagioclase (labradorite) as their chief constituent, with finer layers show the effect of water sorting and quite similar to that of the upper flows was seen, ally appear to have crystallized later than the plagioclase. In some slides a little interstitial quartz and alkali feldspar augite generally second in importance. The other essential resemble ordinary shale or sandstone. plainly overlain by the Ellensburg formation. The constituents are olivine and hypersthene, of which either one are visible.' The mineralogical composition of some of these or both may be present. As accessories there occur abun Relations and age. The Keechelus series is a effort to draw a boundary between this rock and the specimens shows that they are more basic than the specimen dant iron oxide and more or less apatite, and in some slides a lithologic unit, composed mainly of andesites from supposed post-Miocene lava was unsuccessful, since analyzed. little hornblende is seen, which is possibly original, but, on the other hand, may be paramorphic after augite. The which the subordinate amounts of other rocks can the older rock is less altered than usual, probably The pyroclastic pyroxene-andesites are composed augite is of different colors, some being greenish, some brown not consistently be separated. In age, however, it because it consists of massive lava. of fragments that range from less than an inch to ish, and some tinged with violet, indicating its titaniferous has not the unity generally required in a forma In short, the criteria, while sufficient to establish several inches in diameter, the smaller predomi character. The general order of crystallization is apatite, plagioclase, olivine, magnetite, hypersthene, and augite. tion, for while it is mainly Miocene it contains the presence of two distinct groups of these vol nating. In the southern part of the quadrangle The diabase is never quite free from alteration. The feld some material that is almost certainly post-Miocene. canics, fail, except locally, to serve as a basis for the rocks are generally greenish, massive -bedded, spars are commonly somewhat clouded and the olivine is always altered in some degree to iddingsite, which appears The reasons for not separating these should there the determination of boundaries between them. more or less compacted, but not generally hard, also as an alteration product of hypersthene, and may fill fore be stated. On the average, the later andesite is much fresher, and in some places show pseudocolumnar parting. cracks and irregular spaces in the rock. The Miocene dia The lower part of the series, comprising by far less tilted, and less dissected than the earlier, but The larger fragments, most of which are green, base is on the average distinctly fresher than the rock of the Teanaway dikes. its greater portion, consists of a succession of vol in contiguous areas certain phases of the two are so though some are red or brown, show the porphy canic rocks that show considerable alteration. The similar that they can not be discriminated with ritic structure of andesite, but are more decomposed KEECHELUS ANDESITIC SERIES. Keechelus rocks of the northern part of the quad certainty, and the endeavor to map them separately than the material of the lava flows, the feldspars General character and occurrence. The Keeche rangle and most of those exposed in the southern was therefore abandoned. being dull white and the groundmass rather dull lus series occupies most of the western half of the part are of this character. In the basins of Green- Lower in the Naches Valley, in the Ellensburg and earthy. Microscopically, there is seen, in Snoqualmie quadrangle, and is probably the most water and Naches rivers, however, there are some quadrangle, late andesitic lavas occur and have addition to the porphyritic fragments, much finer voluminous assemblage of rocks in the Cascade fresh lavas and tuffs, which are lithologically dis been mapped, since there they are in contact with material, some of the particles showing the char Range for some distance to the west and south. tinct from the more widely distributed decomposed basalt rather than with lava of similar composition. acteristic cuspate forms of glass fragments. It consists mainly of andesitic material, with some rocks. Moreover, the field evidence supports the belief The alteration of the older Keechelus andesites basalt and rhyolite and a small amount of sedi^ The lower and altered portion of the Keechelus that in this area there was little interruption of is interesting, chiefly because its extent varies sig mentary rock. The volcanic rocks comprise lavas, series may without doubt be considered a true geo volcanic activity, so that the necessary grouping nificantly in different areas. In areas at a distance agglomerates, and tuffs, the fragmental rocks prob logic unit, and its Miocene age is evident from its together of the late Miocene and subsequent lavas from the intrusive granodiorite the alteration of ably predominating on the whole, although the relations. In the northwestern part of the quad is not wholly unnatural. these rocks presents familiar features. Changes proportion varies in different localities. In the rangle it overlies the Swank, Teanaway, and Guye Petrography. The volcanic rocks of the series peculiar to the belt of cementation are somewhat northern part of the quadrangle and about Stam formations, and its unconformable relation to all will be described in order of acidity. The rhyolite extensively displayed, and most specimens show pede Pass tuff and breccia predominate, but to of these has been determined by the field work, of the Keechelus series resembles in its essential in addition considerable effects of true weathering. the south lavas are the more abundant. the Keechelus beds generally lying much more characters that of the Kachess formation. It In the northern areas, however, within 2 or 3 miles Classified according to composition, the Keeche- nearly horizontal than the older rocks beneath occurs in the form of breccias and tuffs as well as of the Tertiary granodiorite, where, owing to con lus volcanics are pyroxene-andesite, dacite, rhyolite, them. Seen from a distance it is at some places in flows. Of the massive rock a specimen from ditions of vigorous erosion, weathering is little and basalt, the first two species greatly prepon apparently a capping, and in certain areas the sum the knob east of Pyramid Peak may be considered manifested, the alterations characteristic of the belt derating. mits carved from it are rather flat, their form evi typical. Megascopically, it shows abundant phe- of cementation have proceeded to a remarkable The exposures of the Keechelus series are exten dently being determined by the nearly horizontal nocrysts of quartz and feldspar with a few small extent. sive and fairly satisfactory. They will be briefly attitude of the tuff and lava beds. In the southern ones of biotite, in a dull-white, compact ground- Under the conditions of decomposition obtaining described, beginning with those on the south. part of the quadrangle the Keechelus lavas are mass. On microscopic examination it is found in the southern part of the quadrangle the hyper About the headwaters of Naches and Greenwater overlain by beds of the Ellensburg formation, of that the feldspar phenocrysts are of sodic plagio sthene is most readily attacked of all the minerals, rivers there are excellent exposures of the porphy- late Miocene age, while in the same vicinity the clase, while the groundmass is of quartz and feld and alters to a material having the optical proper ritic lava, mostly grayish black, but in part light Keechelus lava overlies the Miocene Yakima basalt. spar, showing in the same slide micropoikilitic, ties of iddingsite. This material here and there gray, red, and green. Near the head of the South Thus the main portion of the Keechelus series rnicrospherulitic and micropegmatitic textures. partly replaces augite also, but in some specimens Fork of Naches River is a great cliff exhibiting a underlies one Miocene formation and is underlain The dacites are greenish rocks containing abun the monoclinic pyroxene is perfectly fresh while flow of dull-black andesite with columnar struc by others, so that its Miocene age is well determined. dant megascopic crystals of quartz and feldspar. the hypersthene is almost completely decomposed. ture. Tuffs occur, on the whole, in the southern The discrimination of the younger lavas, based Most of the specimens collected are tuffs rich in In a few instances the augite is altering to horn areas in subordinate quantity, but they are exten primarily on lithologic grounds, is supported also crystals. The feldspars are found on microscopic blende. The feldspars are commonly more or less sively displayed near Arch Rock and farther south. by structural and topographical data and one bit examination to be mostly andesine, and the quartz clouded with the usual decomposition products. They are red, green, and yellow in color, and con of doubtful stratigraphic evidence. It is necessary shows the usual phenomena of corrosion. In addi The glass of the groundmass is frequently more or tain many fragments of the porphyritic lava. to give these data and to specify the lithologic tion, the dacites all contain vestiges of phenocrysts less devitrified, the process giving rise1 to minute Pyramid Peak is carved from a conspicuous por evidence. of ferromagnesian minerals, but these are com irregular granules of quartz and feldspar, and the phyritic andesite, but toward the north, along the Lithologically, some of the lava in the Naches pletely replaced by calcite, chlorite, iddingsite, micropoikilitic structure which in some places main divide, the lavas become rather less abundant and Greenwater basins appears as fresh as any that quartz, chalcedony, and epidote, in pseudomorphs occurs may also be secondary. The andesite tuffs than the tuffs. A mass of white porphyritic rhyo might be collected from the slopes of the recently whose forms suggest hornblende and hypersthene. are much more altered than the associated lavag, 9 and the glassy matter once abundant in them has observed in the field and upon the petrographical foothill valleys and plains east of the Cascades it tendency to idiomorphism. The orthoclase, on the contrary, become clouded and largely devitrified. The orig- similarity between the diorite and the Keechelus attains considerable thickness and covers great is interstitial, and often constitutes some individuals of consid o »/ o erable size penetrated .by numerous crystals of the other min inal ferromagnesian minerals in specimens of the andesite. areas, and it is developed extensively through erals, except quartz, which forms anhedra and is in places tuff examined have been completely replaced, West of the head of Lake Keechelus are two out central and southeastern Washington, where intergrown with the orthoclase. ' The hornblende and biotite show no unusual features, the hornblende being of the com except that in some a little augite remains. dikes of hypersthene-diabase which are somewhat it generally rests upon Yakima basalt. Its age mon deep-green variety, and the biotite deep greenish brown. The alterations produced near the granodiorite more basic than the pyroxene-diorite, but whose has been satisfactorily fixed by fossil leaves as late Both show partial idiomorphism. The accessories include apatite, zircon, magnetite, and titanite, which occur in all in the northern part of the quadrangle are made relations indicate that they are of Keechelus age, Miocene, and it is probably equivalent to the "Mas- specimens, and in a few a little allanite appears. apparent chiefly by a general induration, which and these may have been derived from the same call" formation of the John Day basin in Oregon. makes the Keechelus rocks here appear fresher magma reservoir as the diorite. Among its best exposures are those in the Mount The more basic rocks into which the typical than the really less altered andesites farther south. The Meadow Pass area, besides being the most Stuart and Ellensburg quadrangles, and in folios granodiorite locally grades should probably be Their original pores have been filled in, which extensive, is the best exposed. The intrusive mass, 86 and 106 it has been fully described. classed with the quartz-diorites, but it would be makes them more resistant to superficial weather harder than the surrounding volcanic rock, rises In the southern part of the Snoqualmie quad difficult to fix the line between these two species, ing and disintegration. This is especially well like a ruined amphitheater opening to the south, rangle there are a few small areas of conglomerate which are composed of the same essential minerals. illustrated in the tuffs and breccias, which are with its outer walls descending steeply on all sides. that lack fossils to prove their exact age but are As compared with the granodiorites, the quartz- generally indurated and compact. It is believed The inner part of the mass is granular, and the correlated upon lithologic grounds with the Ellens- diorites contain more basic plagioclase, the cores of that this type of alteration is directly dependent granular rock passes gradually into a light-gray burg, which is well developed only a few miles the zoned crystals being sometimes of calcic labra upon the intrusion of the Snoqualmie granodi holocrystalline diorite-porphyry, and this in turn, away, in the Ellensburg quadrangle. The mate dorite. The quartz and orthoclase are even more orite, and the microscopic characters which show at some points near the periphery, into a darker, rial lies in comparatively thin patches upon gently subordinate in quantity in the quartz-diorite than the exact nature of the changes undergone by fine-grained porphyry. On the north side of the sloping surfaces of the Keechelus andesite, with in the granodiorite. The ferromagnesian constit the Keechelus rocks will therefore be considered butte, a short distance from its base, are exposures which it is apparently conformable. The forma uents are in larger proportion; the hornblende in in connection with the description of the grano of a rock which is very similar to the gray diorite- tion is not well exposed and is mapped largely some specimens, but not in all, is more abundant diorite. porphyry in tint and composition, but which shows from loose bowlders upon the surface. Wherever than the biotite, and some specimens contain The basalts of the Keechelus series are mostly a nearly horizontal lamellar parting and a brec- seen in place it consists of an imperfectly consol augite, which is generally much uralitized. similar to rocks of the Yakima and Teanaway ciated structure and has the appearance of an idated conglomerate of andesite bowlders in a light- The granodiorite porphyries show a distinct relationship to basalt formations, already described, and there extrusive rock. No sharp contact could be found colored tuffaceous matrix. The bowlders, which the granodiorites, but, as might be expected, are considerably fore may be passed over without further notice, between this rock and that which is clearly plu- are generally but a few inches in diameter, are well more variable in mineralogical composition than the corre with the exception of one type, which possesses tonic. The mass near Green Pass grades from a rounded. They are mostly of pink or gray hyper- sponding granular rocks. In all, plagioclase is the dominant constituent, quartz occurs in rather subordinate amount, and especial interest. This is a basaltic rock collected light-gray and coarse-grained to a dark-gray and sthene-andesite and include some white pumice. orthoclase is generally identifiable, though often very incon about 2 miles south-southeast of Naches Pass. It finer grained porphyry. At one point andesite All these rocks are abundant in typical exposures spicuous. Hornblende and biotite are in many specimens both present, but some phases contain only biotite. The occupies a comparatively small area, and overlies tuff was seen within a few feet of this rock, but of the Ellensburg formation. texture is as a rule not quite typically porphyritic, for the a great flow of fresh-appearing andesite. It is a the relations were not made out with certainty. grains range in size from phenocrysts to the smallest particles SNOQUALMIE GRANODIORITE. rather light-gray rock containing numerous phe- In the other areas, the contacts are much obscured of the groundmass. Of the phenocrysts, the most abundant and largest are of plagioclase, idiomorphic and distinctly nocrysts of olivine in a nearly holocrystalline by soil and talus. General character and occurrence. Some genet zoned, with cores varying from sodic labradorite to calcic feldspathic groundmass. To sum up, the form of the diorite masses and ically related masses of granular igneous rocks oligoclase, and more sodic rims. Biotite and hornblende when present generally occur as phenocrysts, usually of irregu their relations, so far as observed, are in harmony belonging for the most part to the granodiorite lar outline, and frequently poikilitic. In exceptional cases, Under the microscope, the essential minerals are seen to be with the hypothesis proposed above, although they type, but including more acid as well as more basic quartz also occurs among the phenocrysts. The groundmass plagioclase, olivine, and augite, and the accessories magnetite do not prove it. The evidence derived from the modifications, are exposed in the northern part of usually comprises all the minerals of the first generation with and apatite, while there is very little glass. The olivine, the addition of orthoclase, though hornblende in places occurs which forms the only phenocrysts, shows characteristic crys petrographic study is therefore the more valuable. the quadrangle, mostly about the headwaters of only as a porphyritic constituent. Its texture is usually tal form, modified by corrosion. It has a pale-green tint, Petrography. The granular diorite is medium Snoqualmie River, whose name is therefore adopted microgranitic and of moderately fine grain, but occasionally somewhat deeper on the peripheries and the borders of the quartz forms comparatively large grains poikilitically cracks, which suggests that the color may be partly due to grained and consists mainly of feldspar and dark- for the formation. A small area of this granodio inclosing crystals of plagioclase. Like the granular rocks secondary agencies. It is faintly pleochroic. A very little green prismatic minerals, the general color of the rite also occurs south of Howson Creek. The basic most of the dikes have the composition of granodiorite, but red and green iddingsite has formed at the expense of this rock being greenish gray. The typical porphyry modifications are of very local occurrence, and grade some probably approach diorite. The quantitative composi mineral, and this alteration is the only one which has taken tion of the porphyritic rocks is still more difficult to deter place in the rock. The groundmass contains a second gen is of similar color and contains abundant pheno into normal granodiorite. There is included in this mine by microscopic study. eration of olivine and augite in roundish grains, but its chief crysts of felspar and the ferromagnesian minerals formation, on the other hand, a mass of more sili The biotite-granite forming Snoqualmie Mountain and some constituent is plagioclase. The centers of the roughly lath- of the adjacent heights is more siliceous than granodiorite, shaped plagioclase crystals are of labradorite, while the rims in a finely crystalline groundmass. Some finer ceous biotite-granite, which forms Guye Peak, the much richer in quartz, and free from hornblende. The por are more sodic. The magnetite is noticeably less abundant grained phases are darker and resemble basalt. spur to the west of it, and part of Snoqualmie phyritic modifications of these rocks are more or less similar than in most basalts. Mountain. Its relation to the, granodiorite was in mineral composition to the granular phasss, but show com The best material for microscopic study was taken from paratively large phenocrysts embedded in a finely crystalline The rock has been analyzed chemically by Mr. the Meadow Pass' area, but even the freshest material is con not definitely determined, but it is supposed' to groundmass. The phenocrysts in the granite porphyry are Steiger, with the following result: siderably altered. The essential constituents of both the be derived from the same magma and nearly con of feldspar, biotite, and quartz, the last often noticeably granular and porphyritic rocks originally were plagioclase, rounded by corrosion. monoclinic and orthorhombic pyroxenes, perhaps a little hdrn- temporaneous with it, since granodiorite and gran Analysis of Keechelus basalt. The biotite-granite, when examined in- thin section, is blende, and a little interstitial quartz and orthoclase. As ite show the same relation to the adjacent sediments. found to contain a large percentage of quartz, about an SiO a 50.36 TiO,.. l.i accessories there are moderate- quantities of magnetite and Porphyritic modifications of the granular rocks are equal amount of alkali feldspar, somewhat less oligoclase, A12 O3 ...... 15.83 ZrO a ...... none. apatite. The general order of crystallization has been (1) and a little biotite, largely replaced by chlorite. The alkali Fe8O 8 ...... 2.29 COS ...... none. accessories, (2) plagioclase, (3) pyroxene, and (4) quartz and found on the margins of the large masses, and in feldspar is microperthitic, in contrast with the orthoclase of FeO...... 8.11 P,0«...... 21 orthoclase. dikes. the granodiorite, which is usually not notably perthitic. The MgO...... 7.90 SO3 ...... none. The plagioclase, which shows well-developed crystal form, accessories are magnetite, titanite, zircon, and apatite. CaO...... 9.25 S...... none. is characterized by extremely marked zonal structure, the These granitic rocks are resistant to erosion, and The granite porphyries contain the same minerals as the 3.05 Mo ...... none. central and larger portions of the crystals being of labrador therefore form the summits of several prominent granular rocks, the phenocrysts including comparatively large KS 0... .86 MnO...... 24 ite, and the rims often of sodic oligoclase. It is clouded to peaks, as Chair Peak, Granite Mountain, and Sno crystals of quartz and of both the feldspars, with smaller ones H 80- .05 BaO...... trace. < some extent with kaolin, sericite, and calcite. The quartz of biotite. The microgranitic groundmass contains quartz H 20+. .27 SrO ...... trace. and orthoclase form anhedral grains in the granular rock and qualmie Mountain. Dikes are found n'ear. the and both the feldspars in a second generation. constitute in the porphyries an allotriomorphic granular mix great masses and the connection between the two ture between the microlites of plagioclase and pyroxene in These late Tertiary intrusives, contrary to what the groundmass. The magnetite is largely altered to an can in a few cases vbe directly traced. In other The rock differs considerably from the other basalts of this might be expected, are every where somewhat decom region already' analyzed, being somewhat lower in silica, opaque white "leucoxene," which indicates that it is titan- cases this connection is inferred from the close higher in lime, and, as the large amount of olivine indicates, iferous. petrographic relationship of the dike and stock posed. The feldspars are uniformly at least a little The pyroxenes, which have a tendency to idioinorphism, much higher in magnesia. In the quantitative classification rocks. clouded, kaolin and sericite being the commonest it falls into the subrang auvergnose. especially well marked in the porphyries, are extremely altered, A peculiar rock found in the Keechelus series at several the augite indeed being mostly and the hypersthene entirely Relations and age. The Snoqualmie grauodio- alteration products, though the basic plagioclase,, localities is similar to the "labrador porphyrites" of Rosen- replaced by secondary minerals. In the less altered speci which is more susceptible to alteration than the mens the resulting pseudomorphs are homogeneous and char rite is intrusive in both the Guye and Keechelus busch and the "diabase porphyrites" described by Turner for more alkaline feldspar, sometimes gives rise to the Sierra Nevada, and is probably allied to basalt in compo acteristic. The augite remnants in all slides exhibit the formations, this relation being abundantly proved sition. Megascopically, it has a striking appearance. It is process of uralitization in a very typical manner, and there by observation of actual contacts. Since the Guye complex aggregates of "saussuritic" character. are abundant pseudomorphs of pale-green amphibole which characterized by abundant phenocrysts of feldspar, tabular formation contains Miocene fossils and is overlain The biotite is in nearly all specimens more or in form, with a length often exceeding half an inch, embed in many specimens especially of the porphyries, exhibit the ded in a black aphanitic groundmass. The phenocrysts are characteristic cross section of augite. In places, however, unconformably by the Keechelus lavas, the age of less altered to chlorite, with which epidote often commonly assembled in groups, and in some places intersect there is intergrown with this secondary amphibole some more occurs. Augite, when present, is commonly altered massive, pale-brownish hornblende, which may be original. the intrusive granodiorite must be late Miocene or .so as to form peculiar aster-like figures. in part to uralite. The hornblende, on the con Microscopically, the phenoerysts are found to be labradorite. Quite distinct from the xiralite pseudomorphs are others, post-Miocene. In view of the denudation required The groundmass has an intersertal texture, without flow struc noted in many specimens, of a mineral having the parallel to expose this acid granular rock, which could have trary, is but little altered. Pyrite, supposedly fibrous structure of bastite, but more deeply colored and of ture, and consists of plagioclase laths with secondary ferro attained its holocrystalline texture only under cover, secondary, is of not infrequent occurrence. magnesian material an olive micaceous mineral (iddingsite?) higher double refraction. Since the alteration of hyper and a pale-green amphibole. A similar but much fresher rock sthene to entirely similar pseudomorphs has been observed it appears more plausible to suppose that the intru The chemical character of the Snoqualmie gran was found in association with the Naches sediments in Big very often, there can be no doubt that these represent orig odiorite of the type first described is illustrated by inal hypersthene. sion did not occur much later than the close of the Creek basin. This may be either a flow or a dike of the same the following analysis, by Mr. George Steiger, of age as the Keechelus series. In the groundmass of this rock, In the more altered specimens, however, the ferromagne Miocene. which is probably essentially the same as the one already sian minerals have given rise to more heterogeneous aggre Petrography. The essential constituents of the a typical and fairly fresh specimen from the head gates, which, besides amphibole, and iddingsite, contain described, there is much augite as well as much iddingsite, granodiorite of the prevailing type are feldspar, of Gold Creek: some of which may have been derived from olivine. epidote, calcite, chlorite, and quartz. These secondary min erals also form irregular masses, and sometimes replace por quartz, hornblende, and biotite, all of which can Analysis of Snoqualmie granodiorite. PYROXENE-DIORITE. tions of the feldspars. be identified in hand specimens with the unaided SiO...... 60.49 TiO, ...... 69 Distribution and relations. Within or adjacent The close petrographic relationship of these dio- eye. The feldspar, generally white and semi- A18 O 8 ...... 17.77 ZrO 2 ...... 02 to the Keechelus series, there are several masses of ritic rocks to the typical pyroxene-andesites of the transparent, forms the greater part of the rock. Fe2 O 8 ...... 1.98 CO8 ...... none. FeO...... 3.29 PS O5 ...... 08 granular igneous rock which have for their chief Keechelus series is evident. Even after laboratory The quartz, colorless and glassy, is much less MgO...... 2.94 SO3 ...... none. constituents plagioclase, pyroxene, and quartz, and study of the rocks it is difficult to distinguish some abundant and rather inconspicuous. In promi CaO...... 6.20 S...... none. thus fall within the diorite family as defined by specimens of the peripheral phases of the intrusive nent contrast against these white minerals appear Na,O...... 3.67 MnO ...... 09 K8 O...... 1.37 BaO...... 04 Rosenbusch. The largest of these masses is on the Meadow Pass stock from specimens of the gray the black prisms of hornblende and the dark lus H 2 O at 110° ...... 27 SrO...... 02 main divide near Meadow Pass. Two others lie extrusive andesites found north and west. trous brown foils of biotite, which occur in mod H S O above 110°... 1.13 CoO (NiO?)...... , trace; between Tacoma Pass and Green Pass, and Silver erate and about equal quantity. 100.05 ELLENSBURG FORMATION. Peak is carved from a fourth. These bodies of Microscopic study of the granodiorites shows that the feld This analysis shows a fairly close resemblance to two analy.- diorite are believed to represent the roots of the General character and occurrence. The Ellens- spars include both plagioclase and orthoclase. The plagio ses of the Mount Stuart granodiorite, published in folio 106. volcanoes from which the Keechelus volcanics were burg formation consists of volcanic materials clase, which greatly predominates, generally has more or less As compared with those, it shows about 3 per cent less silica, distinct zonal structure, the cores usually belonging to andes- about 2 per cent more of alumina, the same increase in lime, erupted, the belief being founded upon relations worked over and laid down by water. In the ine, and the outer shells to oligoclase. It shows a strong and a smaller percentage of both the alkalies, but according Snoqualmie. 10 to the quantitative classification it falls in the same subrang, dacites are all considerably altered, the ferromagnesian min direct: effect of heat conducted into the adjacent creeks from their old course tributary to the Yak tonalose. This is in agreement with the similarity, already erals having been replaced by secondary minerals and the rocks. There is possibly no clearer or more strik ima, so that now they flow precipitously through noted, of the two rocks as regards mineralogical composition. glass completely devitrified, while the tuffs have been com The pre-Eocene and late Tertiary granodiorites of this region pactly cemented by secondary material into fairly hard rocks. ing example of this species of metamorphism than a freshly cut canyon to join Denny Creek and are thus practically identical in petrographic character. In one specimen from the ridge south of Silver Peak, calcite this alteration of Miocene rocks by the intrusion of other branches of the South Fork of Snoqual is developed abundantly in irregular masses, evidently replac Metamorphic effects. The intrusion of the Sno- ing portions of the original substance of the rock. In the the Snoqualmie granodiorite. mie Biver. The divide between the head of Coal qualmie granodiorite has produced extensive rock from the side of Lake Keechelus quartz is developed in Creek and these creeks that in pre-Glacial times PLIOCENE (?) SERIES. changes in the intruded rocks. The effects have a similar manner, but in some cases it surrounds a phenocryst formed a part of the Yakima drainage system is so of quartz and has the same orientation as the nucleus, thus HOWSON ANDESITE. been of several different kinds, those most inti showing a mode of growth analogous to the well-known sec slight that the intervening space is largely covered mately related to the intrusion having the char ondary enlargement of clastic grains in quartzite. All of the Occurrence. North and northeast of the head by a swamp. alteration processes seen in the dacites, except those just acters generally recognized as belonging to contact mentioned, are illustrated in the pyroxene-andesites, where, of Howson Creek are two small areas of hornblende- In addition to these morainal ridges there are metamorphism, while there have been indirect owing to the greater areal importance of this rock type, they andesite which can not be correlated with any other glacial deposits which are too ill defined or have been more thoroughly studied. other formation in the quadrangle. This lava too small to map, but which nevertheless afford effects much more widespread and on the whole The general characters of the altered pyroxene-andesites as far greater in amount, seen under the microscope are as follows: The feldspars have was poured out upon an eroded surface of Swauk indications of the length and depth of the extinct True contact metamorphism is exemplified most suffered more alteration than in the areas remote from the sandstone cut by basalt dikes of Teanaway age. glaciers. There are suggestions of morainal topog granodiorite, though they are generally determlnable and strikingly at the Denny and Guye iron prospects, often fairly fresh. They contain secondary inclusions of The relations evidently prove that the andesite is raphy near the mouths of Kachess and Clealum where mineralized zones occur near the contact of various kinds, comprising kaolin, sericite, calcite, epidote, much younger than the Teanaway, but there is valleys, on Naches River near the forks, and in quartz, and scapolite. The phenocrysts of the ferromagnesian nothing to indicate definitely an upper limit to its Yakima Valley near the eastern edge of the quad the granodiorite with the Guye rocks, Magnetite, minerals are usually represented by pseudomorphs, which pre garnet, hornblende, quartz, calcite, and pyrite are sent much variety of composition and structure. Occasionally age. It is much fresher than the lower Keechelus rangle. Bowlders stranded on the sides of the the minerals occurring here, with relations indi one finds regular paramorphs of uralite after augite, and the andesites, and probably is not older than Pliocene once glacier-filled valleys are found at many process of uralitization is clearly exhibited in some specimens, cating that they owe their origin to the presence of but none of the bastite-like pseudomorphs of iddingsite, com or late Miocene. It is noteworthy that the Howson places. East of Lake Keechelus they were noted the hot intrusive magma in close proximity to the mon in other altered andesites, were observed. Generally andesite resembles the rock forming a large pro about 1200 feet above the water level, west of the pseudomorphs are composed of a number of minerals, portion of the bowlders in the Ellensburg forma Little Kachess Lake and south of Howson Creek Guye strata, which here included local beds of including quartz, epidote, amphibole, iddingsite, ealcite, limestone. The presence of the calcareous rock chlorite, and serpentine. In the groundrnasses, no remnants tion, a fact which suggests that the two formations they occur about 1700 feet above the nearest doubtless determined the formation of these con of the original ferromagnesian minerals are found; they have may be of the same age, since the Ellensburg sedi points in the valley bottoms, and some were given rise by alteration to the secondary minerals enumerated tact deposits, which have not been found elsewhere above, finely disseminated in irregular particles, the form of ments were plainly derived from the products of observed about 1200 feet above Yakima Valley, on along the border of the granodiorite. A quartz- the original groundmass crystals not being preserved in pseu contemporaneous volcanism. the knob south of the mouth of Big Creek. These tourmaline contact rock was observed on the South domorphs. In some cases, indeed, the material has in the Lithology. These volcanic areas include no figures, of course, give minimum values for the process of decomposition been so rearranged that even the Fork of the Snoqualmie. porphyritic ferromagnesian minerals have been replaced by tuffs, but consist entirely of lava which shows depth of the valley glaciers at the various points. The direct effect of heat conducted from the formless aggregates. well-developed columnar parting and breaks down Perhaps the most interesting change in these altered andes ALLUVIAL DEPOSITS. magma to contiguous rocks, combined in greater ites consists in the universal devitrification of the glassy base. to form extensive talus slopes. The rock shows or less degree with the effects of heated waters, is The devitrification gives rise to two distinct types of ground- black hornblende prisms and small phenocrysts of The larger valleys have broad floors covered shown by both sedimentary and igneous rocks mass texture, both of which doubtless often arise by cooling feldspar in a dull fine-grained groundmass, which with stream deposits, the most extensive alluvial from a magma, but since both occur more frequently in the within a few yards of the contact. The effects more altered andesites than in the fresher ones, it is consid is usually light gray but sometimes pink. areas being in the northern and eastern parts of thus produced are of familiar kinds, and need not ered that both are also produced by secondary agencies. the quadrangle, along Yakima River and its First may be mentioned the mivropoikilitic texture, which With the aid of the microscope the chief constituent of the be dwelt upon at length. The sedimentary rocks has been described in connection with the Kachess rhyolites. rock is seen to be plagioclase, which seems to belong to three tributaries. Along Clealum River and the Yak have assumed a crystalline structure, and have In this type of groundmass, the plagioclase microlites and the distinct generations. The larger crystals are of stouter habit ima below Easton the stream deposits are well and are more strongly zoned than the smaller, and have abun developed considerable mica, mostly biotite. They ferromagnesian constituents are embedded in comparatively exposed in steep bluffs and consist mainly of large irregular interlocking grains, probably mostly of quartz, dant glass inclusions. In addition to the hornblende there do not, however, exhibit any of the minerals that but probably in part also of orthoclase. In the second and are in the gray andesite phenocrysts of hypersthene, smaller clean, well-rounded gravel. In a railroad cut characterize more intense contact metamorphism, perhaps more usual type, the interstices between the plagio and less abundant. Interstitial between the plagioclase below Nelson, and another 2^ miles above Eas clase microlites are filled with a microgranular mixture of microlites of the groundmass are minute granules which such as garnet, andalusite, or chiastolite. The quartz and anhedral feldspar the latter probably for the appear to be of quartz and orthoclase, and a little glass. ton, silts and sands are more abundant. Gravel alteration of the igneous rocks is illustrated by a most part orthoclase. The hornblende is the most interesting of the minerals. In terraces are well developed in the lower valleys, the gray andesite it is green, with moderate double refraction specimen taken near the contact. It consists of The tuffs of the northern Keechelus areas have undergone especially along the lower Clealum and the Yak alteration similar in character to that seen in the massive and an extinction angle of about 15°. It has the familiar amphibole, feldspar, and dark mica, and although lavas but greater in amount. No glass is found in these tuffs, resorption borders of magnetite and augite. In the red ima near the point where it leaves the quadrangle. it shows no longer the texture of a volcanic rock, although microcrystalline areas with cuspate outlines are andesite the hornblende is of a markedly different variety, The gravel deposits in the eastern part of the abundant, and evidently represent glass particles. The orig with a very small extinction angle, very strong double refrac its composition suggests derivation from a basalt or inal porosity of the rock has facilitated the action of the tion, and a striking pleochroism (j», deep reddish brown; quadrangle, as shown by borings just east of the basic andesite. Another illustration is afforded by heated waters that were probably the principal agent in the \f, lighter reddish brown; ^, light yellowish green). The crys boundary, are of great depth, the bed-rock floor tals generally show narrow borders of hematite, which in a a specimen of altered rhyolite collected near the process of decomposition, and the material has been more being lower there than where the river flows over thoroughly rearranged than in the lavas. The interstices finely divided state is thickly disseminated through the contact on the South Fork of Snoqualmie River. between the fragments, as well as the vesicles of the lapilli, groundmass and gives the rock its color. Magnetite also basalt, several miles down the valley. This is It is mainly purplish drab in color, but contains have been filled with secondary materials, as quartz, horn occurs, however, as hi the gray andesite. Since neither the possibly due to over-deepening by the great val blende, and chlorite, and this cementation has transformed gray nor the red andesite show any marks of decomposition numerous flat, white lenses which might represent the original soft, porous ash beds to hard and compact rocks. the hematite of the latter is doubtless primary. The iron ley glacier. Isolated areas of alluvium in the filled-in steam cavities. Under the microscope the Metamorphosed basalts have been collected on.the north oxide was probably in considerable part peroxidized while tributary valleys, especially along several branches groundmass proves to be a felsitic mixture of slope of Kendall Peak and along the stream which drains the the lava was at the surface and still fluid. The abundance of of Clealum River, indicate similar irregulari Park Lakes. The original basaltic texture is fairly well pre the sesquioxide doubtless determined the formation of brown quartz and feldspar, while the lenses, coarser served. The lath-shaped feldspars are not much altered, hornblende rich in ferric iron. ties in the bed-rock channel. A most striking grained, are of quartz, muscovite, and andalu though always somewhat clouded. The most striking change instance of such erosion is seen above Easton, produced in the rocks is the generally advanced and often QUATERNARY SYSTEM. where a barrier of rock cut by the narrow gorge site, the last two intergrown. complete uralitization of the augite, a phenomenon rarely The remoter effects of the granodiorite intrusion noticed in the basalts collected far from the granodiorite. The Quaternary deposits are classified for pur of the river separates the broad gravel-covered are recognized in the field by the induration of the In the more altered specimens the interstices between the poses of description as glacial and alluvial. They portions of the valley above and below. feldspars are filled in with green amphibole and a finely invaded rocks for a considerable distance from the divided greenish-brown mineral resembling biotite. The are unconsolidated materials, confined mainly to The important gravel deposits of the large val contact. This phenomenon has necessarily already amphibole in some places forms ophitic plates and in others the valley bottoms but usually not well exposed, leys were doubtless formed during and after the fine-grained aggregates. Olivine is not present, nor is it rep retreat of the valley glaciers, by streams over been referred to in describing the Keechelus and resented by recognizable pseudomorphs. Epidote, zoisite, and therefore not readily distinguished from one Guye rocks. It is difficult to ascertain the areal and pyrite are less common secondary constituents. The another. These two classes of deposits are not, loaded with glacial debris. The process is illus extent of the alteration, as the rocks affected by it amygdules of the basalt near Kendall Peak contain quartz, indeed, sharply divided in nature, for they are trated in miniature at the head of the West amphibole, the micaceous mineral referred to, and granular grade insensibly into those which are unaltered. apatite. in some places mingled, and, furthermore, much Fork of Clealum River, where the turbid stream Indurated rocks of this type are to be seen in typi material loosened and carried a distance by draining the glacier on the "7512" peak is form cal development on Alta Mountain, on the north The genetic relation of these changes to the ice has been again taken up and brought to its ing, in the first gently sloping portion of its side of Kendall Peak, along the rim of the amphi granodiorite intrusion has been up to this point present position by water. On the map, where canyon, a long delta of subangular glacial wash, theater at the head of Gold Creek, and on the sum largely assumed, since it could not be satisfactorily the more extensive of the Quaternary areas are over which it flows turbulently, with frequent mit south of Silver Peak, while the dacite breccia discussed before the exact nature of the changes shown, only the material evidently owing its pres shiftings of its channel. along the shore of Lake Keechelus shows effects also was shown. To sum up, these consist chiefly in ent position and arrangement to ice transportation WIND-BLOWN VOLCANIC SAND. attributed to the indirect agency of the granodiorite. the complete devitrification of the glass, the nearly is mapped as glacial. Approximately it may be stated that the changes complete alteration of the ferromagnesian constit Surface material of another type consists of thin GLACIAL DEPOSITS. have reached almost complete development as far uents, and the more or less complete filling of layers of volcanic sand found at many localities in as half a mile from the contact, and are perceptible supercapillary pore spaces. On comparing the Typical moraines are found just below Lake this and other parts of the Cascade Range. Most 2 or 3 miles from it. The nature of the alteration rocks just described with similar rocks of the Kee Keechelus in Yakima Valley, having the form of of these deposits occur on the flat tops of the high will be shown in the following general descriptions, chelus series remote from the granodiorite, it is ridges slightly convex downstream, as is shown on est peaks or in hollows on the slopes, where they which are based chiefly on microscopic study and found that in most of the latter the same changes the map by the topographic contours. These have been protected from erosion. The sand is which may be considered as applying to rocks a have taken place, but to a smaller extent. The ridges are strewn with more or less angular bowlders composed largely of crystals of feldspar and pyrox quarter of a mile from the contact. difference is one of degree rather than of kind. of various sizes, many too large for transport by ene, and its character suggests that it is the finer In the sedimentary rocks, the alteration has nearly all con The agent that has been at work throughout the water. Lake Keechelus and the other large valley portion of material ejected from some volcano of sisted in the filling of spaces with quartz and sericite, prob region is circulating water, and the alterations lakes are held back by moraines, so that the indi the Rainier type and carried by the wind to its ably attended by some rearrangement of the original materials rect effects of these glacial deposits are more appar present position. of the rock. The latter effect, however, has not been con above described are such as are produced by that spicuous. This cementation is a familiar phenomenon and agent below the belt of weathering, in the belt of ent than the small ridges themselves. Two small STRUCTURE. need not be further described. cementation. It is easy to understand how the moraines at the head of Gold Creek that were The alteration of the Keechelus and Guye volcanics has been more extensive than that of the sedimentary rocks, and activity of the water in surrounding rocks would deposited by cirque glaciers are also indicated on Areal distribution of formations. In a broad the metamorphism of volcanic rocks so recent as these is be enormously intensified by the intrusion of a the map. They have been undercut by the tor way the geologic structure of the area is indicated believed to be of peculiar interest. In this alteration there rential streams on either side and the angular by the surface distribution of the rocks of the dif has been both cementation and metasomatism, the latter huge mass of igneous rock. The heat given off having been the more active process in the lavas, while the from the magma would greatly increase not only unsorted material composing them is well exposed. ferent periods, as shown on the areal geology map, two have been, in the fragmental rocks, of coordinate the solvent power of this water, but also the rapid A series of short morainal ridges border the a fuller interpretation of these areal relations being importance. The rhyolites generally have suffered less conspicuous alter ity of its circulation, and thus intensify in a two western side of the swampy area in Snoqualmie exhibited in the structure sections. . A brief state ation than the other volcanic rocks. They are everywhere fold manner its efficiency as a metamorphic agent. Pass. The county road traverses several of these. ment of the areal relations of the formations will thoroughly devitrified, and considerable sericite is usually Van Hise has pointed out that this indirect effect The deposition of glacial gravels in this vicinity therefore fitly serve as an introduction to the dis found in them. Both these features have been noted in specimens gathered at a distance from the granodiorite. The of intrusion is in general vastly greater than the caused the diversion of Guye and Commonwealth cussion of the structure. 11
The pre-Tertiary formations reach the surface in finally, at the close of the Eocene, it became suggest a possible connection with the axis of the quadrangle by smaller masses, the intrusion of four belts. The most northern is in the extreme the southern limb of the Roslyn syncline. In uplift, indicating that the uplift was too great to which is believed to have followed that of the northeast corner of the quadrangle, and the rocks short, these east-west and northwest-southeast be effected by a gentle upwarp of the peneplain, quartz-diorite. here exposed extend 20 miles farther east, forming Eocene ridges of older rock became the axes of so that local adjustment by dislocation became Erosion. Nothing definite can be stated regard the Mount Stuart massif. The next area of old some of the larger post-Eocene anticlines. necessary. ing the age of these igneous intrusions. The near rocks forms ridges north and east of the Kachess The folds in the Eocene rocks are mostly of the In conclusion, it must be pointed out that the est date that is fixed is the beginning of the Eocene, lakes. Another belt of the pre-Eocene rocks com type of gentle flexures. Several anticlinal axes numerous unconformities in this region show that but at that time the granodiorite, serpentine, and poses the bold ridge extending southeastward from can be traced in the large area of Swauk sand the structure is not simple but complex, and its older rocks had suffered a large amount of erosion. Easton, and it is interesting to note that a tiny stone, so that the structure is in no case a simple true interpretation must therefore distinguish The cover under which the granular rock masses island of schist in the middle of Kachess Lake monocline dipping to the southwest, but is rather between the work of distinct periods of defor had consolidated had been removed and the rocks serves to connect, in a way, this belt with the area a succession of open folds whose axes show a gen mation and recognize that the observed structure of varying hardness had been carved so as to form next north. The fourth belt forms the core of the eral southeast trend. The area of Roslyn sand is the resultant of all the movements. There is a region of bold relief. This interval of time, high ridge northeast of Naches Valley, and is stone in this quadrangle represents simply the end not only a striking uniformity in the trend of all during which atmospheric agencies accomplished notable as containing exposures of all the pre- of the large syncline which pitches to the south structural features but there has been throughout so much, is measured by the great unconformity Eocene formations. east. This Roslyn syncline also involves the the Eocene and later periods a persistence in the between the older rocks and the earliest of the Throughout the eastern half of the quadrangle, Teanaway basalt. At Kachess Lake the end of structural axes. These relations are the more note Tertiary sediments. Eocene formations cover the areas intervening the synclinal axis is roughly paralleled by an anti worthy in that these axes, which control both pre- between these belts of pre-Tertiary rocks, except clinal axis, the position of which is indicated by Eocene schistosity and postpeneplain warping, are TERTIARY PERIOD. for a few cappings of Miocene lavas. It may be the small island of schist, and farther west, the transverse to the general trend of the Cascade Early Eocene sedimentation. Conditions favor noted that the youngest of these Eocene forma mountain of basalt, bordered both east and west Range. ing the deposition of the waste from the eroded rock masses began early in the Eocene epoch. tions, namely, the Roslyn and Manastash sand by the underlying rhyolite, marks another syn HISTORICAL GEOLOGYf stones, occupy areas on the extreme eastern margin clinal axis. The latter syncline can be traced Coarse bowlders of granodiorite, serpentine, and of the quadrangle. southeastward nearly to the corner of the quad The geologic history of the area described in this other rocks accumulated near their parent ledges Nearly the whole of the western half of the rangle and as a structural feature is well exhibited folio is largely the interpretation of the facts already and were successively covered with finer sediments. quadrangle is occupied by the Miocene formations, in the vicinity of the peak "6261," where two presented. Three main divisions will be made in Since these contain no marine fossils, it is believed the Keechelus lavas alone covering probably one- sheets of Kachess rhyolite, with the intercalated this geologic history the pre-Tertiary, the Ter that these sands and muds were deposited in the third of the quadrangle. Outliers of the Keeche sheet of Teanaway basalt, form an open syncline tiary, and the Quaternary, all well-differentiated rising waters of a large Eocene lake. The rugged lus lava and Yakima basalt farther east have which passes into a U-shaped fold both to the time divisions in the Cascade province. For the topography caused the coast line to be extremely already been mentioned. This distribution of north and to the southeast. first two of these divisions the available history is irregular, so that inclosed lagoons and narrow the youngest rocks, taken with the areal relations One important structural feature of Eocene date, contained in the rocks, but for the third the inlets doubtless occurred in close proximity to already determined on the adjacent Mount Stuart but affecting Eocene rocks principally, should be record of events is mainly physiographic. bold headlands. The sediments of this epoch were quadrangle, amounts to a roughly semicircular dis mentioned. The dikes that represent the con therefore extremely varied in character, and fine position around Mount Stuart as a center. This duits for the Teanaway basalt flow present a FEE-TERTIARY TIME. muds and coarse granitic sands may have been laid arrangement should be interpreted as indicating a striking parallelism, due to the preexisting joint Formation of the oldest rocks. The oldest rocks down contemporaneously in adjoining areas. The dome structure only in a broad way, but since the system in the sandstone. As studied in this and in the area are probably of Paleozoic age, judging relief of the region is indicated also by the fact that older rocks of this region constitute, in the Mount the Mount Stuart quadrangles these dikes not from their lithologic similarity to those of known the larger part of the Swauk formation is composed Stuart massif, the very highest peaks of the region, only possess this uniformity of trend, but also Paleozoic formations. As has been shown, these of fresh arkose, plainly derived from the Mount the dome conception is of value as a simplified seem to be wholly independent of the folds in rocks are in large part metamorphic that is, they Stuart granodiorite under conditions of active dis expression of the complex structure to be described the Swauk sandstone. Other noticeable characters have been altered from their original condition integration of the granitic rock, with little altera below. in this dike system are the extremely rare occur yet sufficient remains of their original characters to tion of the mineral fragments. In a larger way the Pre-Tertiary rocks. These formations have been rence of intrusive sheets and the almost universal show that the schists, slates, and greenstones of the topographic character of the region in early Eocene subjected to severe dynamic action. So complex absence of local deformation or displacement of Easton, Peshastin, and Hawkins formations repre time is shown by the distribution of the Swauk has been the folding of the three principal forma the sandstone or shale forming the walls of the sent both sediments and products of volcanic activ formation. The absence of this sandstone at sev tions that their true stratigraphic relations can not dikes. When the large mass of intrusive mate ity. Paleozoic rocks strikingly similar to those of eral places where the younger formations overlap be surely determined. The supposition that the rial added to the region in the form of these the Snoqualmie area are found in California, in upon the pre-Eocene rocks, as well as the conspic Easton schist is the oldest formation in the region dikes is considered, this absence of disturbance the Blue Mountains of Oregon, and in the Oka- uous thinning of the Swauk strata in the south is based primarily upon the contrast between its of the walls is remarkable. These facts bear nogan Valley in Washington, south of the inter western portion of the area of that formation, may intensely crumpled and thoroughly crystalline con upon the structural conditions at the time of national boundary. The inference from this well be considered as suggesting the limits of the dition and the comparatively slight alteration of this intrusion. There must have been tension distribution is that during a portion of the Pale Swauk lake at the time of its greatest extent and some of the clay slate in the Peshastin formation. or at least so little lateral pressure that the mol ozoic time the Pacific Coast region, from British the location of prominent ridges that determined The relative age of the Hawkins and Peshastin ten magma could freely open the joints in the Columbia to California, constituted a single geo the shore lines at earlier stages. formations is somewhat in doubt, as has been stated rock, and notwithstanding the introduction of logic province. In the southern half of the area here described above. great quantities of the basalt as well as the accu The absence of Mesozoic sediments in this cen it seems that there existed, in early Miocene time, The schistosity, joint, and bedding structures in mulation of several thousand feet of lava at the tral Washington region suggests that it became a a body of water that was separated from the Swauk the pre-Eocene formations commonly show high surface, no vertical adjustment along these dike land area during Mesozoic time. The existence of lake until near the close of this epoch of sedimen dips, which are often vertical. Over large areas walls was necessary. a thick mass of Cretaceous rocks in the Northern tation. Here the conditions of sedimentation were the strike of these will likewise be fairly constant, Miocene formations. The Miocene rocks, with Cascades immediately south of the international different, since in the Naches lake not only were the northwest-southeast trend prevailing. The the exception of the Guye formation, have been boundary shows the extension of the Cretaceous sands and muds deposited, but basaltic lava flows influence of these structures upon the older intru- but moderately deformed. The strata in the sea southward from British Columbia, while rocks were poured over these sediments from time to time sives can be seen in the rectilinear boundaries of vicinity of Snoqualmie Pass are closely folded, of similar age in the John Day basin and Blue in increasing amount, so that toward the last the the quartz-diorite mass intrusive in the schist and this deformation apparently took place dur Mountains of Oregon mark the southern limit of lavas became thicker than the intercalated sedi southeast of Easton, as well as in the direction of ing Miocene time, since the Keechelus lavas over this central land. Later formations conceal these ments. This was the beginning of the volcanic the serpentine dikes intrusive in the different pre- lying the' Guye formation do not show at all the older rocks over large areas, but future geologic activity that characterized the whole of the Ter Eocene rocks on the next ridge south. same amount of folding. In the large area of the study may furnish data for a description of the tiary. The boundaries of the basin in which the On the geologic map the pre-Tertiary formations Keechelus series dips of 30° and 50° are observed, Paleozoic and Mesozoic geography, which can only Naches formation accumulated can not be deter of the southeastern area, although represented in but, as has been mentioned before, it is difficult to be touched upon now. mined, but, although the Naches strata contain a different colors, are not separated by definite know how much of this inclination may be due to Igneous intrusions. The next recognized event few of the same species of plants that are carried in boundaries. This convention is made necessary initial slope of the lavas. in the geologic history of the region was the injec the shales of the Swauk formation, yet it is note by the difficulties encountered in attempting to The axes of post-Miocene uplift will be described tion of large masses of molten rock into these older worthy that the two basins, though closely adja delimit these formations in the field. In some under the heading "Historical geology." It is suf rocks. The schists, slates, and greenstones of the cent, were the scenes of very different geologic portions of the Manastash and Taneum basins the ficient here simply to note the identity of these with Easton, Peshastin, and Hawkins formations had activities, In the Swauk lake there was appar thick mantle of soil contains small fragments of the axes of Eocene and earlier folding, especially been folded and uplifted from their original posi ently no interruption of quiet sedimentation until slate, serpentine, and green schist, indicating that with that marked by the high ridge north of tions when the intrusions of igneous rock began. near the very close of the epoch, while in the these rocks underlie the surface in complex rela Naches River. The persistence of this structural The earliest of these was that of the extremely basic Naches basin during the same time there were tions. In the absence of data for drawing even axis is noteworthy. magma which crystallized to form the peridotite, successive eruptions of basaltic lava. rough boundaries the areas have been colored on Faults. A few small faults can be detected in now largely altered to serpentine. In the north The result of the deposition of these sediments the map with the tint appropriate to the rock the Swauk formation, especially near its contact eastern part of this area this intrusive rock cut and the accompanying lava flows would have been predominating in the soil. with the older rocks in the northeast corner of across the older rocks and so divided the complex to efface the earlier topographic diversity had not Eocene formations. In considering the structure the quadrangle. More important faults occur on of sedimentary and volcanic rocks that their orig other geologic forces been active. The erosion of the Eocene rocks, it is of prime importance to the high ridge north of Naches River. Two of inal disposition can not be determined. In the unconformity at the base of the overlying Tean realize the influence of preexisting structure and these border the syncline already described, while southern region the basic intrusive simply filled away basalt makes it probable, however, that local the topography determined by it. Study of the another is of sufficient throw to bring the Miocene small fissures so that the dikes of serpentine now elevation and gentle flexing of the rocks terminated varying sections of the Swauk sediments clearly basalt against the pre-Eocene rocks, the basalt at observed are narrow and relatively unimportant. the epoch represented by the rocks of the Swauk indicates that the areas of schist which extend into the base of the slope dipping 35° toward the older The next intrusions were of a different character. and Naches formations. the area of Swauk sandstone not only represent formation. A large body of dioritic magma was forced into Volcanic eruptions. Erosion had commenced anticlinal axes, but mark as well the position of old At its southeast end, near the edge of the quad the Easton schist, its boundaries being largely the work of truncating certain of the folds in the Eocene ridges which outlined and separated the rangle, this last-mentioned fault appears to be of determined by the structural planes in that meta Swauk and Naches strata when volcanic activity different Eocene basins. So too, the ridge of schist recent date. The freshness of the scarp and its morphic rock. To the north, in the area closely began on a larger scale. Even before the basaltic and diorite south of Yakima Valley formed the relation to what appears to represent the old low adjacent to this quadrangle, the Mount Stuart eruptions in the Naches basin ceased, flows of rhy- boundary between the Swauk and Naches basins in land surface strongly support the conclusion that batholith of granodiorite represents an intrusion olitic lava were poured forth in the same area, with early Eocene time and also the southern limit of this faulting occurred during the uplift of the on a large scale, its main mass measuring many the result that the lowest sheets of Kachess rhyolite Roslyn sedimentation in the late Eocene, and range. The position of the fault and its direction square miles in area and being represented in this are intercalated with the Naches sandstone and Snoqualinie. 12 basalt. Later flows of the same lava, probably diabase representing the old conduits can be seen effective over a much larger area than that in which Quaternary time. The uplift of the Cascade from a southern center of eruption, extended where the older rocks underlying the basalt are there is reason to suspect the presence of intrusions Range inaugurated the present cycle of topo farther north and covered the Swauk sediments exposed. The dikes, however, are not so numerous of this age, so that it is more probable that the graphic development, and it may be said that along their western edge. Owing to its high melt as those which fed the Eocene basalt flows. localized intrusions and the broad mountain uplift the commencement of this widespread deforma ing point, the rhyolitic lava became viscous soon These lava flows were poured forth over a are simply concomitant manifestations of the same tion marked the end of the Tertiary, or with after reaching the surface, so that the rhyolite did region having considerable relief, but the surface earth forces. equal probability it may be stated that this warp not spread out like the basalt in horizontal flows, inequalities were soon obliterated by the floods of More definite statements can be made regarding ing and uplift were events of late Pliocene time but appears to have consolidated into thicker molten rock which filled the deepest depressions the depth at which this granular rock crystallized which continued into the Pleistocene. masses, even taking the form of low ridges or and lapped over the higher portions of the old sur than are usually possible. Apparently only two The character of this mountain uplift can be mounds with moderately steep sides. face. Eventually the region, which before had formations constituted the cover of the batholith determined by a consideration of the physiography Before the rhyolitic eruptions ceased, basaltic been diversified with verdure-covered hills and over most of the area that has been mapped. In of the region. The distribution of the high peaks lavas again spread over a large area. In the valleys, became a monotonous waste of black rock. the portion of the granodiorite mass at the head of in the Snoqualmie quadrangle is believed to give a southern part of this quadrangle these flows were Miocene sedimentation. Possibly contempora Gold Creek the Keechelus andesitic series alone is clue to the nature of the uplift of this portion of less important and the sheet of basalt associated neous with the basalt eruptions there was sedi present as the intruded rock, and since, so far as the range. If only elevations of 5000 feet and with the rhyolite flows probably represents the thin mentation in the northwestern part of the area can be determined, no other formation has overlain over are considered, it will be noted that these fall margin of the Teanaway basalt which was erupted here described. The Guye formation includes this volcanic series in this portion of its area, a into three groups. The southernmost of these from the fissures to the northeast. In the north grits, sandstones, shales, chert, and limestone, close approximation to the depth of the intrusion groups lies on both sides of the main divide and ern region, however, these eruptions were on a sediments deposited in a basin whose extent is not in this locality seems possible. Here the peaks extends both east and west beyond the boundaries large scale, the whole area being covered with suc known, since these strata have not been recognized composed of the horizontal lavas rise not over of the quadrangle; the group next northward com cessive lava flows, which in places reached a total except in the vicinity of Snoqualmie Pass. Asso 2000 feet above the highest contact with the gran poses the high ridge forming the divide between thickness of over a mile. ciated with the sediments are flows of both basalt ular granodiorite, which is 2000 feet above the Yakima and Naches rivers; while the third line This volcanic material reached the surface and rhyolite, again affording striking evidence as base of the Keechelus series in this vicinity, and of heights is near the northern edge of the quad through hundreds of cracks in the sandstone, to the constant recurrence of eruptive activity, an additional 2000 feet would seem, with all the rangle. The trend of these elevated regions is serpentine, slate, and other rocks. For the most even at a distance from what seemed to be the observations in mind, a very reasonable estimate slightly north of west, or nearly at a right angle pa,rt the lava spread out in great sheets, while in main centers of volcanism. of the amount eroded from such peaks, inasmuch to the main drainage divide of the range. Since certain localities the presence of steam in the The Guye strata were soon subjected to extreme as this allows an original thickness of 6000 feet for uplift has outstripped general degradation in the molten rock appears to have caused explosive dynamic action and closely folded. The marked the Keechelus series in this part of the area. The development of the mountain range, this arrange eruptions, thick beds of basaltic tuff being inter alteration of these rocks is not due wholly to this intrusive mass therefore reached within 4000 feet ment of the areas of topographic prominence may calated with the lava sheets. folding, since later intrusions were probably more of the upper surface of the volcanic rock. The be taken as indicating the positions of the areas Later Eocene sedimentation. The violent volcan- effective in their metamorphism. intrusive rock in this vicinity retains its uniform of uplift. ism was generally succeeded by quiet sedimentation Later Miocene eruptions. Erosion had begun to granular texture close to the contact, although The possibility that the prominence of the three in the later part of the Eocene. Sedimentation attack the rocks of the Guye and other Miocene dikes extending upward into the overlying rock lines of heights is due to selective erosion rather began in the western parts of the area before the formations when another epoch of widespread vol exhibit the usual change in texture. The slow than to differential uplift is opposed by the fact last flows of Teanaway basalt were erupted and in canism was inaugurated. This differed from earlier consolidation of the intrusive magma must have that both stream and glacial erosion have been the sandstones and shales thus intercalated in the eruptions in that the lavas were largely andesitic, been favored by the presence of residual heat in and are most active in their attacks upon the basalt fossil leaves are found that afford evidence although both basaltic and rhyolitic phases occur. this mass of late Miocene lavas. northern heights, while along the lower part of that farther west the conditions favored forest The eruption of the Keechelus andesitic series was Uplift and erosion. The presence of local the north-south divide the common occurrence growth. A land area must have existed, therefore, on a large scale, possibly exceeding in importance unconformities between the various Tertiary for of a thick mantle of soil shows how much less between this and the Puget basin, the sediments of that of the Teanaway basalt, and even in some mations is proof of uplift and erosion at different effective are the agents of transportation there which contain the same flora. degree comparable with that of the Yakima basalt. times. The latest events in this period were doubt than on the slopes of the higher east-west ridges. The sands and muds deposited in this later Eocene Dikes leading up to these flows, similar to those less of the same character, differential uplift pro Although the highest peak in the area the epoch appear to have been better sorted than the associated with the Eocene basalt, are not common, ducing gentle folds, on the arches of which the "Needles," 7512 feet is mad.e up of the resistant materials composing the earlier Eocene sediments. but the lavas and tuffs of the Keechelus series rocks Avere exposed to erosion. In the Ellensburg metamorphosed Keechelus lavas, yet the next Vegetal matter, like that present in the earlier for appear to have been erupted from volcanoes whose quadrangle, which is immediately southeast of the highest peaks, in the northeast corner of the mations, now became prominent, and during the sites are marked by the areas of pyroxene-diorite. Snoqualmie quadrangle, there is conclusive evi quadrangle, are composed of relatively soft ser later part of the epoch represented by the Roslyn Although the lavas and tuffs of this series cover dence of moderate flexing of the Miocene forma pentine; and again, the low part of the main formation the conditions of sedimentation were nearly a third of this quadrangle, this area repre tions and their reduction to an approximately level divide at Stampede Pass is in exactly the same such as to allow the deposition of several beds of sents only a small part of their extent to the south plain, or peneplain, to which a Pliocene age has rock as the high country farther south. From carbonaceous material, which now furnish workable and west. These volcanic rocks accumulated over been assigned. these relations it would appear that rock charac seams of coal. this area to a thickness of several thousand feet, The absolute identification of this Pliocene low ter has not been a controlling factor in determin Sedimentation during Eocene time appears to and the volcanoes from which the material issued land surface is difficult outside of the region border ing the location of the heights. The conclusion have taken place in basins that were neither exten may have been active throughout the rest of Ter ing the valley of the lower Yakima River. In the appears warranted that the uplift of this portion sive nor permanent. The relation of the Swauk tiary time, or, indeed, into the Quaternary, when heart of the range it can not be recognized, and of the Cascade Range took the form of three and Naches lake basins has already been referred the neighboring cone of Mount Rainier began to the only places in the Snoqualmie quadrangle well-defined upwarps, transverse to the axis or to; and in the latter part of Eocene time the Ros be built up. where the old surface may possibly remain are trend of the range, considered in its whole extent. lyn waters did not extend far to the south, since At one locality a lens of sedimentary material in the southeastern corner. On the high ridge Two of these axial uplifts ex-tend, eastward and the basal sediments of the Manastash formation, occurs in this Keechelus series, showing that the north of Naches River, near the head of the connect with similar elevated regions. The north which is of later Eocene age, rest directly upon volcanism was not continuous, and the fossil leaves South Fork of Manastash Creek, there are level ernmost line of heights is thus continuous with the the pre-Tertiary schists. The deposition of the found in the shale indicate that these interludes tops, which are eroded on rocks of different for prominent Mount Stuart massif, which forms the sands and muds, which have now become indu were long enough to permit vegetation to become mations, and are strikingly different from the axial portion of the supposed Wenatchee Moun rated and form the rocks of the Manastash forma established in the vicinity. surrounding topography. These exceptional topo tain upwarp of the peneplain; and the ridge tion, closed the Eocene sedimentation so far as the The occurrence of several small areas of typical graphic forms are strongly suggestive of the Plio between the Naches and the Yakima finds its record is known. Ellensburg gravels upon the surface of the Kee cene peneplain, recognized 10 or 15 miles to the topographic continuation in the Manastash and
Earlier Miocene eruptions. The stratigraphic chelus lava affords evidence that in late Miocene southeast. v», Umptanum ridges in the Ellensburg quadrangle, break between the Eocene and Miocene epochs time the streams that distributed fluviatile material Resume. In the Cascade province, the Tertiary which are known to represent upwarps of the old indicates a time of erosion in this area. Only in over the lower country to the southeast deposited period was essentially a time of volcanism. Erup lowland surface, the evidence being cited in detail the southeast corner of the quadrangle is the record a part of their burden here. It seems, indeed, tion closely followed eruption, the basaltic floods in the Ellensburg folio. To the east these upwarps at all complete. Here the rocks of the Manastash probable that the volcanic material of the Ellens- in the Naches basin continuing even while the die out in the Columbia Plain, so that the trans formation were somewhat folded after their deposi burg sediments may have been in part derived, by flows of rhyolite were poured forth over the same verse uplifts may be considered as details in the tion late in the Eocene. Erosion followed, and erosion, from portions of the Keechelus lavas. area, and the lava streams being in turn quickly broad uplift of the Cascade Range, which trends this was continued for a considerable time, to be Intrusion of granodiorite. No exact date can be covered by molten basalt in the northern area. approximately north-south. terminated by a recurrence of volcanic activity, the assigned to the granitic intrusion in the northwest Thus the lavas erupted in Eocene time from differ Development of present topography. The broad eruptions of the Eocene being only a prelude to ern part of the quadrangle. The Snoqualmie gran ent centers united to form a thick mantle of vol configuration of the Cascade Mountains is the the volcanism of Miocene time. odiorite plainly intruded the Guye formation and canic rocks over the larger part of the region here direct result of the uplift just described, and it The Miocene volcanic activity opened with the Keechelus series, both of which are of Miocene age. described. Between these eruptions sediments is further argued that this direct relation of topo eruption of the Taneum andesite, a relatively The intrusive mass contains many cubic miles of were deposited in local basins, but often the proc graphic prominence to uplift extends even to many unimportant formation. Immediately after this, material, the area covered by it extending far esses of sedimentation were interrupted by the of the minor features, yet the relief as we see it however, came the eruption of the Yakima basalt, beyond the Snoqualmie quadrangle. The trans encroachments of lava flows. During the Mio to-day is the result of the active work of degrada which was poured forth over a vast area, the west fer of this large amount of molten rock into strata cene, andesitic lavas alternated with basalt out tion that was inaugurated when the uplift of the ern margin of which comes within the Snoqual- of Miocene age must have produced orographic flows, while beneath the surface large masses of peneplain began. This work of sculpturing the ele mie quadrangle. The basaltic eruption during results that were much more important than magma were intruded. In adjacent areas and vated rock masses into the present land forms has the Miocene epoch constitutes one of the greatest the local metamorphism of the intruded forma probably in this quadrangle as well, this volcanic continued throughout Quaternary time. Owing to of known volcanic phenomena. The mass of these tions. The amount and kind of the contact action activity extended into the Quaternary. the heavy precipitation in the area here considered, basalt flows, which extend beyond the boundaries can be directly observed, and has been described in erosive processes have been very efficient, and the of the State of Washington, is measured in terms an earlier part of this folio, but the broader influ QUATERNARY PERIOD. relatively young range, which owes its origin to so of thousands of cubic miles, and the transfer of so ence of the batholithic intrusion upon the structure Main uplift of the Cascades. The later uplift recent an uplift, is already characterized by matu great an amount of material from the earth's inte of the Cascade Range can only be surmised. Its of the lowland surface just referred to was undoubt rity of topography. rior to the surface ranks as one of the greatest geo occurrence so late in the Tertiary period, which edly connected with the 'birth of the present Cas The processes of rock disintegration and of detri logic events. However, these eruptions were for probably closed with the uplift of the mountain cade Range. This was perhaps the closing event tus transportation have been so energetic over most the most part unmarked by violence, being of the range is suggestive, although the statement that of the Tertiary period, but present knowledge of of this area, especially its more mountainous por nature of a quiet upwelling of fluid lava from a this intrusion had a causal relation to that uplift the later history of this area is too incomplete to tions, that in a broad way the varying resistance of number of vents. Dikes and intrusive bodies of would hardly be justified. The Cascade uplift was Warrant a sharp separation between Tertiary and different rocks appears to have been an inefficient 13
factor in determining the general topographic form. main valley, and it thus marks the line of escape to Analyses have been made of samples of the diameter and associated with it are masses of pyrite Rugged and high peaks of sandstone or serpentine the southeast for the waters which accumulated Roslyn coal from a series of openings extending crystals. Through oxidation of the pyrite the rock may overtop ridges of basalt, while broad, glaciated along the side of the glacier. from the Clealum mine through the Roslyn mine forming the sides of the gulch is coated with iron valleys cut across the hardest as well as the softest Connected with this epoch of glaciation was the to the northwestern extremity of the basin. These oxide, which makes the indications of the extent of formations. Yet, in the development of topo deposition of the gravels and silts of the valleys. analyses, which were furnished by L. S. Storrs the iron ore somewhat deceptive. At another graphic detail, rock character is a modifying if The increased precipitation which is believed to and are given below, show the variation in this opening on this property, pure magnetite forms not a controlling factor. have characterized this epoch greatly augmented seam from a lignitic, noncoking coal to a fairly a vein-like body with parallel bands of massive Stream history. In outlining the part played by the general degradation of the region, and large good coking coal. The samples are numbered garnet and of calcite. The magnetite appears to the streams of this area in the development of the quantities of rock detritus were then contributed in an order that represents the localities at which be the oldest and the calcite the youngest of topography, little can be said of the streams trib to the streams. This loading of the transporting they were taken, beginning with the open part of these crystallizations. Surface workings on the utary to Puget Sound, as their history has not waters was so complete that when the gentler the fold, beyond the edge of the Snoqualmie quad mountain slope expose what are apparently large been, worked out. The master eastward-flowing grades of the lower valleys were reached the rangle and continuing toward its more steeply bodies of this magnetite, but these bodies are found streams, Yakima and Naches rivers, have been streams were unable to move the whole of their inclined portion within the area described here. to be oval lenses, 20 feet or more across, which lie studied in their lower courses. The Yakima load and thus began to aggrade their beds. These The, change in the coal is therefore considered approximately parallel to the surface and thus established its lower course before the uplift of gravel deposits are much more extensive along the as an expression of the increase in the amount exhibit maximum exposures of the ore. the peneplain and maintained it, while Naches main Yakima Valley, where their thickness must of dynamic action as the heart of the Cascade The Guye iron prospect is due north of Sno River is believed to be antecedent in a part if reach hundreds of feet. Since these glacial gravels Range is approached. The coking tests show qualmie Pass, on the west side of the shoulder not in the whole of its lower course. In the Sno were deposited the principal stream work has been- that the best. coking coal comes from the por connecting Guye Peak with Snoqualmie Mountain.; qualmie quadrangle the drainage appears to have the reexcavation of the valleys. This has been tion of the field included within the Snoqualmie The magnetite deposit here is near the contact a mixed character as regards its relationship to the effected only to a slight degree, and along with quadrangle. The coal from the western part of between the granodiorite and the Guye formation. uplift of the region. The Naches is for the most this has gone the deposition of sediment at the the field is also reported to be much better adapted The intruded rock here is limestone, and similar part consequent, in that it follows the line of upper ends of the lakes. The silting up of the for gas making than that from any of the other limestone or marble also occurs near the Denny depression between the two axes of uplift men large lakes from this cause has been sufficient to localities. prospects, so that the general relations are essentially tioned above. The upper Yakima likewise occu be noticeable, especially at the place where the Analyses of Roslyn coal samples arranged numerically the same at the two occurrences of magnetite. At pies an area of relative depression, and this position deposits of two streams have caused the separa from east to west through the basin. the Guye prospect garnet is associated with the may explain the notable fact that its broad low- tion of Kachess and Little Kachess lakes. magnetite, stringers being seen extending through Sample. Moisture. Volatile matter. 1 the ore band, which is much wider and more con grade valley extends so far back into the heart of' Ash. Character of coke. the range. The history of the most important ECONOMIC GEOLOGY. .. !§&* stant than in the occurrence on Denny Mountain. tributary of the Yakima, Clealum River, is less Large blocks of fairly pure ore can be taken out COAL. simple. This river appears to head somewhat 1 4.69 38.89 44.27 12.15 Sinter. here. north of the northern or Wenatchee Mountain The most valuable mineral resource of Kittitas 2 4.39 38.61 47.28 9.72 Strong sinter. Analyses of these magnetites, made by Professors 3 7.07 axis of uplift, and has deeply dissected the ele County is coal. The Roslyn basin, the western 3.50 40.35 49.08 Cokes. Shedd and Fulmer, show that the ore is high in 4 2.12 37.64 48.13 12.11 Fair coke. iron 62 to 68 per cent and low in silica and vated region in the northeast corner of this quad end of which lies within this quadrangle, is one 5 2.02 88.17 47.25 11.56 Fair coke. rangle. This position of the Clealum must have of the most productive coal basins on the Pacific 6 2.13 86.77 46.48 14.62 Good coke. sulphur, with . phosphorus practically absent. been antecedent to the uplift, which was so grad Coast. The coal occurs in the upper part of the 7 1.87 32.19 44.55 21.39 Very strong coke. The presence of pyrite in some of this ore would ual that the stream has maintained its course with Roslyn formation, and the extent of this pro doubtless make much of it carry a considerable no essential change since the time it flowed across ductive portion, together with the location of Two small mines are operated at the western end content of sulphur. Notwithstanding this the ore the Pliocene lowland. mines, is shown on the economic geology map. of the Roslyn basin. The coal mined here is of is of satisfactory quality, but so far these two prop The drainage of this area therefore appears to be The upper beds of the formation have been eroded good thickness, but contains a heavy clay parting erties have not been developed, owing, no doubt, in part dependent upon the position of the axes except in the center of the basin, so that the coal in the middle of the seam. The product of these to the uncertainty whether the magnetite occurs in of uplift and in part independent of it, the can field is limited to the vicinity of Ronald and mines is mostly shipped by rail to points in eastern sufficient quantity. yons cutting directly across the regions of maxi thence extends eastward into the Mount Stuart Washington. The origin of this magnetite at the contact of mum elevation. This variation in the amount of quadrangle. The outcrop of the Roslyn coal can Prospecting for coal has been carried on in the the intrusive granodiorite is undoubtedly more or agreement between drainage and deformation may be traced along the northern side of the basin, but vicinity of Coal Creek near Snoqualmie Pass, less directly connected with the intrusion. The be due to the fact that the later or post-Pliocene on the southern side the deep gravel filling con where the Guye formation includes some dark, association of minerals and the position of the warping followed to some extent lines of earlier ceals the rocks beneath and the mapping of this carbonaceous shales. At several points on the deposits strongly favor this view. The relations deformation, so that streams which previous to the boundary of the basin is based wholly upon data mountain between Keechelus and Kachess lakes observed at the Guye tunnel suggest replacement of peneplanation had adjusted themselves to the earlier derived from general observations of the structure the sandstones and shales interbedded 'with the the limestone by.the magnetite and the garnet, and structure might appear to be consequent upon the made elsewhere. As shown on the map there are Teanaway basalt have also attracted prospectors the date of this mineralization may very plausibly warped surface, although in reality they are ante about 4 square miles of possible coal lands in the for coal, but here also, while the rock is leaf be referred to the later stages of the granodiorite cedent to this later warping. Snoqualmie quadrangle. bearing and black, the indications of coal are intrusion. At the Denny prospect the abun Drainage modification has been effected to some The structure of the Roslyn basin is simple. very slight. The other dark leaf-bearing shales dance of pyrite may indicate that the sulphide was extent within this quadrangle. The most notice The dip of the coal beds is low, 10° to 20°, and in the Eocene and Miocene formations, other than deposited along with the oxide. In one specimen able example of capture of the headwaters of one no faults have been ' discovered in the basin as the Roslyn, contain little to justify prospecting for of metamorphosed wall rock both pyrite and mag stream by another'is at Snoqualmie Pass. Com Studied in this and the Mount Stuart quadrangles. coal. The conditions under which these sediments netite occur, and under the microscope the magnet monwealth and Guye creeks were evidently once As can be seen from the geologic map, which were deposited were not favorable to the accumu ite can be seen in small grains along cracks in the tributary to Coal Creek and thus formed a part of shows the areal distribution of the Roslyn and lation of carbonaceous material in sufficient amount rock and in finer grains bordering the larger grains the headwaters of Yakima River. Glacial obstruc underlying Teanaway' basalt, the axis of this to form coal seams. of pyrite. It seems doubtful, however, whether the tions at the Pass, however, caused the diversion of basin pitches to the southeast, and since the fold most of the magnetite could have been derived from IKON. their waters westward into the South Fork of Sno is somewhat unsymmetrical, with lower dips on the sulphide, since sulphur is wholly lacking in the qualmie River. So low is the divide in the swampy its northern side, the axis of the basin is nearer The absence of any large deposits of Iron ore on analyses of the Guye ore and no pyrite was noted area of the Pass that it would require very little the southern edge. Thus the deepest portion of the Pacific Coast has stimulated prospecting for there. That there has been a slight amount of engineering work to divert these waters again into the shallow basin in this quadrangle is probably iron in Washington. Among the localities in subsequent concentration of the ore is shown by their original course. along the line of the Northern Pacific Railway which deposits of iron minerals have been found, one case of brecciation of the massive garnet with Glaciation. Evidences of glacial action are con between Ronald and Roslyn, two of the more promising are within the area of impregnation by the magnetite. fined to the northern half of the Snoqualmie quad Several beds of coal are known in the Roslyn the Snoqualmie quadrangle. The only magnetite Clealum River area. The Clealum iron ores are rangle. The existing glaciers near the northern basin. The principal one of these is the Roslyn deposits in the State occur in the vicinity of Sno different, both in character and origin, from those edge of the quadrangle have already been men seam, which is most extensively mined at the town qualmie Pass, while the iron ores on Clealum River of the Snoqualmie Pass localities. They outcrop tioned. These are remnants of large glaciers for of that name, half a mile east of the edge of this are of poorer quality, but occur in larger bodies. in low hills or "iron buttes" along Clealum River which the high mountains in this region formed quadrangle. In fact, many of the workings of the Snoqualmie Pass area. The magnetite deposits between Camp and Boulder creeks and on the ridge the center. The longest lobes of this% ice mass Roslyn mine, the largest in the State, are within near Snoqualmie Pass show many of the charac south of Boulder Creek. The ore bodies occur as extended southward as three ice streams, which the Snoqualmie quadrangle, although the shaft and ters of contact deposits. The location of these lenses at the basal contact of the Swauk sandstone from their approximate relations to present drain principal works are at Roslyn. The Roslyn seam deposits at or near an intrusive contact and the on the serpentine. The field relations as well as age lines may be called the Keechelus, Kachess, Was earlier mined from works at Ronald, but now characteristic contact minerals associated with the the character of the ore indicate that it is of sedi and Clealum glaciers. These were glaciers of the this place is almost deserted. The annual product ore favor this view as to their origin. The Denny mentary origin, being a peculiar basal phase of the alpirie type and were important agents in modify of the Roslyn and Clealum mines, which are oper prospect is located on the western slope of Denny Swauk formation. ing the preexisting topography, widening and ated by the same company, is about 1,000,000 tons. Mountain, about 2 miles west of Snoqualmie Pass. The iron ore is a greenish-black, dull rock of deepening the upper valleys considerably. The The Roslyn coal is a coking bituminous coal, The country rock here is the Snoqualmie grano- amorphous appearance. It is characterized by the topographic features due to glaciation have already well adapted for steam raising and gas making. diorite near its contact with the intruded Guye for occurrence of numerous oolites in the structureless been mentioned under the heading "Relief." The It is an excellent fuel for locomotives, and over mation. The mineral deposits which have been matrix. It contains both magnetite and hematite, four large lakes in this quadrangle, as well as one-half of the product of this field is sold for prospected as iron ore constitute a mineralized associated with more or less weathered serpentine, scores of smaller ones, owe their existence either railroad consumption. The cleanness of the coal band rather than a distinct vein. The granodiorite and the ore lenses are composed of masses which to glacial excavation or to damming by glacial and its high percentage of lump fit it well for is much jointed and the joint planes are coated vary from, concentrated ore, containing 55 per cent deposits, most of them to both. Probably all shipment. Naval tests have shown that the with hornblende and garnet crystals. In the gulch, or more of metallic iron, to the clayey waste of three of these glaciers reached the main Yakima Roslyn coal ignites quickly, combustion being where some exploration work has been done, a com serpentine. Valley at some time in their history. South of rapid and thorough, the coal swelling slightly plete section of the ore-bearing band can be seen. Analyses of ore from six different properties in Easton a ridge about 1000 feet high immediately on the surface of the fire. The percentage of The band is parallel to one of the principal joint this area indicate an iron content ranging from 46 borders the valley and back of this ridge there is a ash is moderate, and the clinkers formed do planes, trending a little west of north, and has on to 58 per cent, but average samples would doubt well-defined valley, parts of which are now trib not cling to the grate bars, except with forced its west side a bed of massive garnet, in places less run lower. A large sample was collected by utary to several streams. The most plausible expla draft. The amount of soot formed and the high 10 feet wide. Next to this are garnet, quartz, Mr. Bailey Willis, for the purpose of procuring nation of this exceptional feature seems to be that temperature in the uptake are the only objection green hornblende, and calcite, all well crystallized. material for a representative analysis. This sam this side valley was eroded when ice occupied the able features of this coal. The magnetite occurs as nodules 1 foot or less in ple was taken to represent an exposure of 350 Snoqualmie. 14 square yards, and its analysis by Dr. Hillebrand In a few localities development work on veins Near the northern edge Of the quadrangle a poses shows that further development of the fer follows: containing ores of gold, silver, and copper has prospect located on the fault contact of the Kee- tile lands in Yakima County must depend upon chelus lava with the serpentine shows mineraliza Analysis of iron ores from "iron buttex" along Clealum River. been sufficient to secure some recognition of these improvements in water storage. The many lakes local areas as mining districts. This exploration tion of the crushed rock with stibnite present as of the Snoqualmie area constitute a natural storage ...... 7.50 NiO.. .20 TiO8 ...... 70 MgO 2.30 work is still being prosecuted, yet little can be the principal ore mineral. basin for the Yakima. The three large lakes, A1,O, ...... 21-90 H 8 O 6.80 stated regarding the future value of these pros Gold Creek district. Although the Gold Creek Keechelus, Kachess, and Clealum, are well adapted O8 0a ...... 2.20 .09 basin lies in a region that is accessible for only a Fe,0s ...... 37.10 S... .03 pects. In describing these developments, the for future utilization and have been surveyed as FeO...... 21.80 coa .15 subject must be treated largely by areas, for few months in the year, several small mines have possible sites for storage improvement. MnO...... Undetermined, a little. none of the ores are distinctively of a single been opened in it. At the Esther and Louisa In the elevated portions of this area the snow 100.27 metal. claims, on the eastern side of the amphitheater at banks remain until late in the summer, and thus Metallic iron. 42.51 The vein deposits of the Snoqualmie quadrangle the head of Gold Creek, two tunnels have been help to maintain the summer flow of the streams. The Clealum iron ore is thus seen to be of low occur both in the pre-Eocene greenstone and gran driven. These are near the wide granodiorite dike On this account it is essential that the mountainous grade and its high percentage of alumina indicates odiorite and in the Eocene and Miocene lavas and that cuts the Keechelus series. The vein contains tracts that have no other value be protected espe that it would also prove refractory. granodiorite. In all of the localities where these pyrite, ruby silver, galena, and sphalerite, but even cially from the sheep-grazing industry, which has These ferruginous bodies originated as residual veins occur there is evidence of crushing and frac the sphalerite contains some admixture of the silver already seriously injured the region. Desolate deposits on the surface of the serpentine, which turing of the rocks as well as of igneous intrusion minerals. The pay ore occupies only a portion of tracts of burnt timber and rocky slopes where was exposed to weathering before the Swauk in the vicinity. In view of the small amount of the width of the vein, and the best ore shipped is sharp hoofs have cut up the turf, allowing the soil epoch. Conglomerates of either granodiorite or exploration of the veins the observations are neces reported to have carried 240 ounces of silver and to be washed away, mark the track of the sheep serpentine bowlders occur elsewhere at the base sarily too limited to warrant definite statements as f 10 in gold. herder. Such conditions can not fail to affect the of the Swauk formation and represent simply to the relative importance of the different agencies Below the prominent bench in this amphitheater natural storage of the water in the mountains, and local phases that are somewhat coarser than these in the deposition of the vein minerals. It may be is another property on which considerable work thus to diminish the supply available in midsum deposits. Where inclosed basins were formed in noted that the veins are confined to the compact has been done. This belongs to the Cascade Min mer for irrigation along the lower valleys. serpentine rocks, the residual material covering igneous rocks, and it seems probable that the frac ing Company, and the principal development con the surface would receive drainage charged with tured nature of the rock has been the determining sists of a tunnel that crosscuts the granodiorite to SOILS AND FORESTS. iron and decaying vegetation, thus furnishing condition of mineralization. This relation is com intersect the vein, which is also developed above Agriculture within the Snoqualmie quadrangle solutions of such character that the work of con monly recognized by the prospector. by a shaft. This vein, like the vein on the other is confined chiefly to the alluvial soils. These centration may have begun early in the Eocene Camp Creek district. The most important and property, has a north-south trend. The values are areas of alluvium are outlined on the areal geol epoch. thoroughly prospected district is the northeast cor in lead, silver, gold, and copper, and a wide zone ogy map. They include the terraces and bottom The analysis given above supports this explana ner of the quadrangle. In 1899 and 1902, when of mineralized granodiorite exposed in the tunnel lands bordering the larger streams and rivers. In tion of the ore as the product of decay of the the survey of this quadrangle was made, active also shows a small percentage of copper. such tracts the alluvial soils exhibit considerable serpentine. On comparing the analysis of the development work was being done at several small Other prospects. Copper prospects have been variation in texture. Fine silts, easily cultivated ore with the analysis of the serpentine of this mines in the vicinity of Camp Creek. Three of opened along the canyon of the Middle Fork of and very fertile, cover the bottom lands, but coarse, area it is found that the ore is simply a rearranged these, the Maud O., the Ida Elmore, and the Snoqualmie River. Here bornite and chalcopyrite well-washed gravels occur in other localities, and but chemically little modified residual product. Clealum tunnel, are located on veins in the Haw- occur with quartz crystals in pockets in the Sno these are comparatively barren. The presence of chromium and nickel shows its kins greenstone, and another, the Edna R., is in qualmie granodiorite. All of this quadrangle was originally wooded relationship to the serpentine. The occurrence of the granodiorite. In all these mines the veins are Several prospect mines have been worked at except some of the highest and most rugged peaks. alumina in this ore in excess of silica indicates near the contact with the serpentine, and at the different times on the creek northwest of Little Even these bear scattered trees having the stunted that a free oxide or hydrate must be present. Maud O. there appears to be a zone of crushed Kachess Lake. These are on veins, many of and gnarled forms that are characteristic of forest This chemical resemblance to the ferruginous Hawkins greenstone into which the pyroxenite has which are poorly defined, in the schist, the sand growth in localities where the struggle with snow bauxite ores is in accord with a certain physical been intricately intruded. At the Ida Elmore, a stone and slate, and the granodiorite. Pyrite, and wind is severe. The lower valleys, however, similarity, seen in the presence of the oolitic serpentine dike cuts the greenstone, while at the chalcopyrite, bornite, and arsenopyrite occur as once contained the finest specimens of forest trees. structure. Other analyses have shown also that Clealum there is a dike of granodiorite-porphyry. the ore minerals, associated with quartz and The red fir and white cedar attained here their per the oolitic phases of the ore are much richer in The veins are not as a rule regular, and even epidote. fection of growth, and the stand of timber in these alumina than are the more massive portions of where the walls are well defined the vein may be valleys was originally very heavy. Most of this WATER SUPPLY. the ore. badly pinched in places. The veins show such a timber, however, has been cut to supply the mills Considerable exploration work has been done variety in trend that no system can be made out Since the annual precipitation in this region along Yakima and Green rivers, and fire has dev in this area to test the extent of these ores. If for the group. The ore minerals are pyrite, and everywhere exceeds 40 inches and probably reaches astated other tracts, so that little remains to indi followed by underground workings the ore stra arsenopyrite in rusty quartz. Some good values 100 inches in the higher part of the range, this cate the former extent and magnificence of these tum exposed in the valley would be fonnd to dip in gold have been reported, but when the district quadrangle is well supplied with perennial streams. forests. Over much of the area of this quadrangle under Goat Mountain at angles ranging from 30° was visited none of the properties had become A slight amount of irrigation is practiced at a few the rugged relief and the distance from the rail to 60°, but the nature and origin of the deposit indi producers. points along the Yakima Valley, but the value of road would prevent any use of the timber for cate that this stratum could not be expected to be Cinnabar has. been found in a prospect on the the water supply of this area concerns a wider ter lumbering, so that, the forest might be preserved very thick or as continuous as a coal bed. The eastern edge of the quadrangle at the head of ritory. This quadrangle includes the most impor without difficulty if- fires could be prevented. ridge ore deposits would dip south at a higher angle. Boulder Creek, where it occurs along a joint plane tant portion of the headwaters of Yakima River, Over 50 square miles in the southern part of the in the altered rock of the Peshastin formation. and the economic value of this river in its relation quadrangle is included within the Mount Rainier OTHER METALLIFEROUS DEPOSITS. The richness of the ore is evident, but the thin to irrigation in the lower valleys can not be overes Forest Reserve. The greater part of the area of this quadrangle ness of such bands of cinnabar may prevent the timated. The fact that the waters of the Yakima has been thoroughly explored by the prospector. deposit from being of economic importance. are at present wholly utilized for irrigation pur May, 1905.