Cenozoic Rocks of the Santa Rita Mountains, Southeast of Tucson, Arizona By HARALD DREWES

GEOLOGICAL SURVEY PROFESSIONAL PAPER 746

A systematic descTiption) augmented by 19 mdiometTic age deteTminations) of one of the most complete sequences of Cenozoic Tocks in southeasteTn ATizona

UNITED STATES GOVE R NMENT PRINTING OFFICE, WASHINGTON: 1972 UNITED STATES DEPARTMENT OF THE INTERIOR

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY

V. E. McKelvey, Director

Library of Congress cata log-card No. 72-600158

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D .C. 20402 - Price $1.50 (paper cover) INTRODUCTION 3 which lie between the Santa Rita Mountains and the some of the intrusives of group 3 are probably as­ Patagonia Mountains to the southeast (fig. 1). A sociated with the magmatic events of the Helvetian small part of the northeast end of the Santa Rita phase, or late phase, of the Laramide orogeny. They Mountains extends outside the Sahuarita quadrangle, are briefly described in this report, to preserve the however, and is not described here. continuity of the discussion of geologic events, but The geologic units described here are all younger inasmuch as they are ancillary to the major plutonic than the Piman phase (Drewes, 1969), or main masses of the Laramide, they will be described more phase, of the Laramide orogeny. They consist of fully in another report I am preparing on the (table 1) (1) some volcanic and clastic rocks de­ plutonic rocks. posited between the two local phases of the Lara­ The geologic investigation of the Santa Rita Moun­ mide, during Paleocene (?) time, (2) several dike tains is part of a larger program of the U.S. Geo­ swarms and associated plugs, of Paleocene age, (3) logical Survey to map and interpret the geologic stocks of granitoid rocks and intrusives of quartz history of all the ranges i'oughly between Tucson latite porphyry, also of Paleocene age, (4) quartz and Bisbee (fig. 1). Many geologists are involved veins, volcanics, plugs, and dikes, of Oligocene to in this program, and most of their field studies are Paleocene age, (5) volcanics, laccoliths, and dikes, completed. Cooper (1970) has mapped the Sierrita of late (?) Oligocene age, and (6) assorted gravel Mountains; Finnell (1971)", the Empire Mountains; deposits and soils flanking the mountains. At least Creasey (1967), the Whetstone Mountains; R. B.

TABLE 1. - S mnrnal'y of Cenozoic rocks of the Santa Rita Mountains [ Broken lines indicate that the adjacent formations are contemporaneous or that the ir relations are uncertain]

Age Rock unit Description Thickness (feet) Youngest gravel Gravel a nd intercalated sand on floor s of m odern wa tercou rses. 0-100± Cobble to pebble gravel and inter calated sand; capped by infa ntile 0-200± Holocene Gravel facies gray soil. Low-level terrace ----- depos its Silt and loam of the Santa Cruz River terrace ; capped by infantile 0-200± Silt facies gray soil.

~ capped by " Late Intermediate-level pediment and Boulder to p ebble gravel, grit. and intercalated sand; 0-400± "c.> terrace deposits weakly developed thin reddish-brown soil. ~ '0; Boulder to pebble gravel and intercalated sand; locally cem ented; 0-50± 0: Middle High-level pediment deposits capped and overlapped by well-developed thick red soil.

Piedmont fac ies Cobble to pebble gravel. grit, and inter calated sand a nd silt; com- Pleistocene m only pinkish gray, slightly indurated, and locally well cem ented. 0-2,00O± and Bas in-fill gravel ------Pliocene - - Ri-ver- fac-ies - W ell-sor ted cobble to pebble gravel and sand. locally cem ented. 0-300± Tuff beds V ery Ji g ht g ray rhyolitic tuff and tuffaceous sandstone. 0- 20 Pliocene Cobble to pebble g ravel. which is rich in volcanic clasts, and tuffa- and Gravel of N ogales ceous sand and s ilt, w hich is pale red to brownish g ray, poorly 0-1,000± Miocene sorted. a nd slightly indurated. Rhyolite intrus ives of the northern Rhyolite porphyry of a plug and of two dike swarms; locally a Santa Rita Mountains brown v itrophyre. ------Dikes a nd stock of the Rhyodacite porphyry dike s warm and m oderately coarse grained :5~" San Cayetano Mountains light-gray granodiorite. 'QP; - -Dik-es a----nd laccoliths in-- the Rhyodacite v itrophyre intrus ives, medium-gray to light-gray. Late ( ? ) ~ E ~ Grosvenor Hills area ...... ): .... ------Oglicene - - Rhyodacite sU3~ m ember Rhyodacite Java fl ows, agglom erate, tuff, and welded t uff. 150-2,200 8 E6 Grosvenor ;g~~ Hills Rhyolite 500+ m ember Rhyolite tuff and a little welded tuff and lava. o~ V olcanics "~ 0" Gravel a nd Pale-red s ilt and gravel ,,,ith well-rounded pebbles; includes som e ~ rn 0- 200 s ilt member shale and f resh-water limestone. Quartz vein swarm Mineralized quartz veins of the southern Santa Rita Mountains. Oligocene Rhyolitic volcanics Rhyolitic tufT a nd lava( ?) of W asp Canyon. 0-100 to Paleocene Olivine andesite p lugs V esicular a nd a m ygdaloidal olivine andesite of Deering Spring. A nd esitic dikes Andesite. dacite. a nd diorite dikes, s ills, and some small pipes. Quartz latite porphyry dikes and plugs. light-gray to g rayish- orange-p ink ; phenocrysts; GreatervilIe intrus ives contains stubby bipyramidal quartz associated with base- and noble-metals enrichment ; plugs arc am eboid s haped. Medium-dark-gray m edium-coarse-grained quartz diorite. Paleocene H elvetia ~uartz~ i o rite_ Lig ht-gray m ed ium-coarse-grained stocks of granodiorite to quartz stocks Granodiorite monzonite com position; elliptical shaped. Cottonwood Canyon dike swarm Quartz latite porph yry, fin ely porphyritic to coarsely porphyritic. Li g h t~br own i s h.gray very fine grained g ranodiorite in core of a Plugs of Gringo Microgranodiorite plug. Gulch area -- - - - Dacite porphyry H ornble nde dacite, m edium-dark-gray, locally coarsely porphyritic. V olcanics of Red Mountain Intensely altered rhyolitic a nd andesitic pyroclastic rocks. ------[------Rhyolitic to dacitic tuff, w elded tuff, tuffaceous sandstone, and a Paleocene ( ?) Gringo Upper member capping andes ite lava flow. 900 + Gulch . V olcanics Lower m ember Rhyolitic a nd dac itic pyroclastic rocks and som e fl ows; contains intercalated epiclastic rocks. 700 + 4 CENOZOIC ROCKS OF THE SANTA RITA MOUNTAINS, ARIZONA

Raup (unpub. data, 1971), the Canelo Hills; Simons and Mesozoic history. The basic data appear on the (1971a, b), the Patagonia Mountains; Hayes, the geologic maps, first open-filed in 1966 and 1968 and Huachuca Mountains, and Raup, the Mustang Moun­ now published (Drewes, 1971a, c), which will be tains (Hayes and Raup, 1968); and Hayes and referred to frequently. Some collateral reports on Landis (1964), the Mule Mountains. geochemistry of the area and on stratigraphy are

ACKNOWLEDGMENTS now or will soon be available (Drewes, 1967, 1968, 1971b; 1972a, b; Hayes and Drewes, 1968; Simons The collateral work produced through a larger and others, 1966). program of the U.S. Geological Survey has provided The oldest known rocks of southeastern Arizona both supporting and restraining data for the inter­ are the Pinal Schist, which generally includes some pretations of the Cenozoic geology of the Santa Rita gneiss and migmatite. The schist is most extensive­ Mountains. However, the Cenozoic record is less ly exposed and best studied in the Little Dragoon complete outside the Santa Rita Mountains than Mountains, where Cooper and Silver (1964, p. 11- within them, so the validity of the interpretations 23) described it in considerable detail as a sequence on correlation and environments of deposition has at least 20,000 feet thick of metamorphosed con­ generally not been widely tested. Nevertheless, some glomerate, sandstone, siltstone, shale, and rhyolite of these interpretations were developed jointly with and basalt lava flows. They further described the my colleagues, whose assistance is gratefully ac­ major aspect of this sequence as a "cyclic gray­ knowledged, and will also be applied to geologic wacke-slate lithology," which contains "graded bed­ situations in adjacent areas. The interpretations ding, the intercalated lava flows, and the abundant here are thus not necessarily the results solely of my volcanic debris." L. T. Silver (oral commun., 1968) efforts; yet the validity of their local application dated a rhyolite flow as 1,715±10 m.y. old using the remains my responsibility. . U-Pb isotopic method on a suite of zircon samples. The success of the field investigation was facIl­ The thickness and lithology of the Pinal Schist were itated by many people. Invaluable assistance in map­ interpreted by Cooper and Silver (1964) as indic­ ping and sampling was provided by G. C. Cone, ative of geosynclinal deposits. Some aspects of this Bruce Hansen, C. W. Norton, F. W. Plut, J. R. geosyncline were reviewed by Anderson (1951, Riele, R. A. Rohrbacker, Albert Sutheimer, and W. p.1345). M. Swartz between 1963 and 1968. Discussions in In the Santa Rita Mountains, schist and gneiss the field with R. E. Wallace, M. D. Crittenden, Jr., that have been correlated with the Pinal Schist form J. H. Courtright, and P . H. Pickard helped to clarify inclusions, roof pendants, and remnants of wall­ some problems and to raise others for which I am rock of large granitoid plutons of Precambrian and particularly grateful. The courtesies of George younger ages. The schist and gneiss are inconse­ Bradt, Roy Green, Dewey Keith, and George Yakob­ quential as detrital components of the Cenozoic ian, residents near the Santa Rita Mountains, and clastic deposits of the mountains. of Profs. John Anthony, D. L. Bryant, Evans Mayo, Extensive masses of coarse-grained and porphy­ and S. R. Titley, at the University of Arizona, and ritic alkali granite, quartz monzonite, or grano­ of E. S. Davidson, M. E. Cooley, Fred Pashley, and diorite occur in many of the ranges of southeastern S. C. Martin, of various government offices, are Arizona in which the Pinal is exposed. The batho­ also acknowledged. liths and stocks intruded the Pinal and commonly Invaluable support was obtained from many lab­ metamorphosed the schist along their contacts. oratories. Some radiometric dates were obtained Several of these granitoid masses have been dated from Prof. P. E. Damon before their publication, by the U-Pb, Pb-alpha, and Rb-Sr methods. Based and many other dates were provided by R. F. Mar­ on these dates and on geologic relations currently vin, T. S. Stern, S. C. Creasey, and their colleagues. being studied, intrusives in southeastern Arizona The numerous chemists and spectrographers who are probably representative of two older (1,650- have contributed are acknowledged in the tables 1,760 m.y.) magmatic episodes and a younger included in this report. G. C. Cone also ably assisted (1,430-1,460 m.y.) magmatic episode (Silver, 1969). in many phases of the general preparatory work. In the Santa Rita Mountains much of the base­ GEOLOGIC SETTING ment rock is the Continental Granodiorite, a The geologic record of the development of the coarse-grained porphyritic granodiorite and quartz Santa Rita Mountains during the Cenozoic Era monzonite with a radiogenic date of 1,450 m.y. but follows a fragmentary record of the Precambrian possibly older. One sample of this rock was dated history and a more extensive record of the Paleozoic by Rb-Sr and by Pb-alpha methods as Precambrian, INTRODUCTION 5 but another sample, dated by the K-Ar method, volcanic rocks, of Mesozoic age, lie unconformably records only a Laramide thermal event (Drewes, upon the Paleozoic and Precambrian rocks of the 1968, p. C5). This rock characteristically disaggre­ Santa Rita Mountains (Drewes, 1971b). The lowest gates upon weathering to form grus and gritty sequence, of Triassic rocks, consists of rhyodacite detritus that is a widespread component of the volcanics and some eolian sandstone and conglom­ younger deposits in the northern part of the erate of the Mount Wrightson Formation and of mountains. red beds and some volcanics and conglomerate of the Rocks of the Apache Group of Precambrian age, Gardner Canyon Formation. The middle sequence, although absent in the Santa Rita Mountains, are of Early Cretaceous age, consists of rhyolitic to present in areas a few miles to the northeast, and andesitic volcanics and of coarse conglomerate of they shed light on the geology of the Santa Rita the Temporal and Bathtub Formations, overlain by Mountains at that time. The Apache Group un­ arkose and conglomerate of the Bisbee Group; the conformably overlies the Pinal Schist and the Apache Canyon Formation of the Bisbee Group granodiorite masses, and it is intruded by diabase contains also a little intercalated marine limestone. of Precambrian age. The stratigraphic sequence of The highest sequence consists of the Fort Crittenden this group is probably most complete in the Little Formation of Late Cretaceous age, which also con­ Dragoon area, where it was described in detail by tains arkose and conglomerate, and the overlying Cooper and Silver (1964, p. 36-41). But even there Salero Formation, which is made up of coarse con­ the upper of the three formations comprising the glomerate and abundant dacitic and rhyodacitic group, as present farther to the north, is absent. volcanic rocks. The Santa Rita Mountains were The total absence of the Apache Group in the central intruded by monzonitic stocks of Triassic age, by and southern parts of southeastern Arizona, in­ a large granite stock, the Squaw Gulch Granite, of cluding the Santa Rita Mountains, and the absence Jurassic age, and by several stocks of quartz diorite of the upper third of that group in the northern to quartz monzonite of late Late Cretaceous age. part indicate either that during the Precambrian The Mesozoic geologic history of the area is more these areas remained sufficiently high so as not to complex than the pre-Mesozoic geologic history. Soon receive sediments during all of Apache time or, after the beginning of continental conditions, the more likely, that they were uplifted and the top of area was strongly faulted, and volcanics and red the Apache deposits was eroded. beds filled some large basins. Late during the Tri­ The Precambrian geologic history of the area assic, the rocks were faulted again and were intruded thus includes an early time of sedimentation, orogeny by Piper Gulch Monzonite. These events are possibly and attendant metamorphism and batholithic in­ distant and slightly delayed effects of the Sonoran trusion of at least one episode, further sedimen­ Orogeny, proposed by Fries (1962) . Further volcan­ tation, and diabase intrusion and minor crustal ism was followed, near the middle of the Jurassic, disturbance. by the intrusion of a large granite stock and by The Precambrian rocks of the Santa Rita Moun­ strong uplift. During the Early Cretaceous, vol­ tains are unconformably overlain by a sequence of canism was resumed locally, along with the deposi­ Paleozoic shallow marine deposits 5,000-6,000 feet tion of conglomerate at the foot of block-faulted thick. The sequence extends from the Bolsa Quartz­ mountains. The finer clastic rocks deposited later ite of Middle Cambrian age to the Rainvalley Forma­ during this time indicate a waning local relief and tion of late Early Permian age. Limestone and possibly some subsidence. An arm of a continental dolomite are the most common rocks of the sequence, sea briefly encroached upon the area and deposited but clastic rocks are fairly abundant near its bottom the limestone beds. and top. The continuity of the sequence is broken A final major geologic event preceded the deposi­ by several disconformities, of which the largest tion of Cenozoic rocks and began during the Late represents at least most of Ordovician time and all Cretaceous, perhaps as long as 90 m.y. ago (Drewes of Silurian time. and Finnell, 1968, p. 315; Drewes, 1969). Initial The Paleozoic geologic history of the area is one tectonic activity was recorded by a coarsening of of alternating marine transgressions and regres­ the epiclastic deposits, a resurgence of volcanism, sions, reflecting successive epeirogenic movements. and the appearance of unconformities in the strati­ Toward the middle of the Permian Period the area graphic column. Before the close of the Cretaceous was uplifted more strongly, and continental condi­ these rocks and older rocks were strongly thrust tions became prevalent. faulted and folded, and then they were invaded by Three thick sequences of continental clastic and a group of granitoid stocks. These stocks are (1)

472-410 0 - 72 - 2 6 CENOZOIC ROCKS OF THE SANTA RITA MOUNTAINS, ARIZONA a large stock of Josephine Canyon Diorite, mainly descri bed under the section "Volcanics of Red a medium-coarse-grained rock of diorite to quartz Mountain," are extensively exposed in the Elgin diorite composition but also containing a late quartz and Lochiel quadrangles to the east and southeast. monzonitic phase; (2) smaller stocks of coarse­ In outcrops the Gringo Gulch Volcanics are typi­ grained Elephant Head Quartz Monzonite; and (3) cally composed of light-colored and flat-lying or a composite stock of coarse-grained Madera Canyon gently inclined massive units. Although most of the Granodiorite. I have briefly described these rocks tuffaceous rocks are only moderately well indurated previously (Drewes, 1968). Collectively, these events and rather friable, a few bedded units are strongly are referred to as the Piman phase of the Laramide indurated and form small cliffs, ledges, and buttes orogeny, which is the earlier and stronger of the that contrast markedly with the gently rolling hills two phases recorded southeast of Tucson. characteristic of the weakly indurated tuffs. In ad­ The sedimentary and volcanic rocks deposited dition to the indurated bedded units, many pods of after the Piman phase, and described in this report, silicified rock near the Narrows along Sonoita Creek, are summarized in table 1. The oldest of these 3-4 miles southwest of Patagonia (fig. 2, loco D), rocks was intruded by both plutonic and hypabyssal form knobs and east-west alined rock ribs. Most of masses and was deformed during the Helvetian the tuffs are very light gray to very pale orange, phase, the younger and weaker subdivision of the some are darker gray or bluish gray, and a few are Laramide. variegated in pale pink and green. The few andesitic PALEOCENE AND P ALEOCENE(?) ROCKS lava flows of the formation are brownish gray, and the dacitic and andesitic epiclastic rocks are green­ Two groups of rocks of the Santa Rita Mountains ish gray or bluish medium gray. are largely or wholly of Paleocene age. The older group consists of a sequence of volcanics and some STRATIGRAPHY A:,\D PETROGRAPHY intercalated epiclastic rocks assigned to the Gringo The Gringo Gulch Volcanics consist of many Gulch Volcanics, of Paleocene (?) age, and a small lenticular units which are divided on a stratigraphic mass of highly altered volcanic rock assigned to an basis into the lower and upper members. Both unnamed unit, here referred to as the volcanics of members are composed largely of rhyolitic tuffs and tuff breccias; the upper member is distinguished by Red Mountain, also of Paleocene (?) age. The young­ a basal bluish-gray partly welded tuff and some an­ er group of rocks consists of small stocks, plugs, desitic flows, whereas the lower member contains and dikes, which commonly are of porphyritic tex­ some dacitic flows and epiclastic rocks derived from ture and of latitic to dacitic composition. Some of the dacitic volcanics. intrusives have associated mineralized rocks. Radio­ The formation overlies an unconformity of moder­ metric dating of some of these intrusives indicates ate relief. To the north, along Gringo Gulch (fig. that they are Paleocene. 2), the two members lap unconformably over rocks GRINGO GULCH VOLCANICS of the Lower Cretaceous Bathtub Formation The Gringo Gulch Volcanics (Drewes, 1968, p. (Drewes, 1971b) , which is one of the formations C14) are a sequence largely of rhyolitic to dacitic mapped as older rocks (Mesozoic) in figure 2. To tuffs 1,500-2,000 feet thick that unconformably the south, between Sanford Butte and locality A in overlies rocks as young as the Salero Formation and figure 2, rocks of the lower member lap against the the Josephine Canyon Diorite, both of late Late Josephine Canyon Diorite and some older rocks, Cretaceous age. The scanty available geologic data, such as the Salero Formation (Drewes, 1968, and described later, suggest that these volcanics were unpub. data). Although the actual contact of the deposited before about 55 m.y. ago, at which time volcanics with the diorite is everywhere covered they were intruded, altered, and in places min­ because of the friability of the volcanic rocks, that eralized. contact is believed to be depositional rather than The volcanics underlie an area of at least 6 square intrusive because the volcanics are neither contact miles in the southeast corner of the Mount Wright­ metamorphosed nor included in the diorite, as is the son quadrangle near Patagonia (fig. 2), and they slightly older Salero Formation. Furthermore, in probably underlie an additional 4 square miles a few places conglomerate lenses in the lower beneath a cover of gravel within the quadrangle. member of the Gringo Gulch Volcanics contain dio­ The volcanics also extend southward into the N 0- ritic clasts that could have been derived from the gales quadrangle (fig. 1), and their probable cor­ Josephine Canyon Diorite, although sparse alterna­ relatives, the volcanics of Red Mountain, which are tive sources are also available.