Description of the Spanish Peaks Quadrangle

DESCRIPTION OF THE SPANISH PEAKS QUADRANGLE. GEOGRAPHY. the plateau portion is subject to frequent summer Timpas formation. The Timpas and Apishapa always arranged parallel with the bedding. The showers, and in the neighborhood of the peaks formations, both of which are characterized by entire formation is soft and easily eroded, and the The Spanish Peaks quadrangle is bounded by thunderstorms accompanied by heavy rains are of the presence of limestone strata, or of shale con resulting surface is gently undulating except meridians 104° 30' and 105° and parallels 37° and frequent occurrence. taining a considerable proportion of lime, consti where the protection afforded by intrusive sheets 37° 30'. It is 34.5 miles long north and south, Along the narrow valleys of the Purgatory and tute the Niobrara group and are elsewhere mapped of lava has tended to form low mesas. The out 27.5 miles wide east and west, and contains 950 Apishapa, cultivation is carried on by means of undivided as the Niobrara formation. The Nio crop extends about one-half the length of the square miles. It lies mostly in Las Animas irrigation. But all the higher valleys brara beds are distinguishable by their limy quadrangle in the northeastern portion, with two -, , Agriculture. County, Colorado, but part of it about 28 square and mesas ol the central and western character from all other Cretaceous formations, small areas in the vicinity of Trinidad and another miles in the northern portion ; is situated in portions can generally be cultivated successfully except the Greenhorn limestone of the Benton somewhat larger area near the southwest corner, Huerfano County, the divide separating the Pur without irrigation, and there is a belt several miles group, from which, however, the limestone of the the total area approximating 120 square miles. gatory and Apishapa drainage from that of the wide around the base of the peaks that is largely former is readily distinguished by its color and Trinidad sandstone. The Trinidad sandstone Cuchara being the common boundary. Except under fence, where wheat, oats, rye, maize, timothy, fracture. represents some part, or possibly the whole, of in a comparatively small area lying to the potatoes, and ordinary garden vegetables are sure The Timpas formation comprises about 200 the Fox Hills ongroup, but on account of Character northeastward, the surface is hilly and mountain crops with natural moisture only. feet of strata, of which the lower 45 to 50 feet is its relation to the Laramie and the o?thextent ous. The chief topographic feature is the saddle- limestone and the remaining 150 feet calcareo- thickening of the lower zone of the for- Tnnidad> GENERAL GEOLOGY. shaped£ mountain in the northwestern Topographic_ .. argillaceous shale interrupted by thin limestone mation northward it is presumably the upper portion generally known as the Spanish features- SEDIMENTARY ROCKS. bands, which become prominent toward the top. portion only. In the Spanish Peaks quadrangle Peaks, though called by the Indians " Wahatoyas," The limestone at the base is made up of layers, the total thickness is about 150 feet in the vicin in allusion to the fancied resemblance to a woman's In the geology of the Spanish Peaks quadrangle usuallyJ less than 12 inches thick,' which Limestone.. in ity of Trinidad, and 170 feet toward the north breasts. (See fig. 5, on Special Illustration sheet.) the Archean and Paleozoic eras are not represented are separated from one another by very the TiI"Pas- boundary. As elsewhere, the formation consists The culminating points are about 3 miles apart, by any formations that reach the surface, though much thinner layers of calcareous shale. The of a basal zone of thin-bedded, fine-grained, dark- West Peak, which has an elevation of 13,623 the former, if not the latter, may be assumed fracture is conchoidal and rudely parallel with the gray sandstone layers, separated from one another feet, being 915 feet higher than East Peak. The to underlie the whole of the area. The oldest bedding planes, and the grayish-white weathered by thinner partings of shale; and an upper zone mountain rests upon a broad platform that falls exposed sedimentary rocks are probably part of surfaces break off naturally into thin conchoidal of massive, light-gray sandstone, capped by a few gradually toward the east and terminates in a the Morrison formation (Juratrias), but they are flakes. As the Greenhorn limestone is dove feet of brown sandstone in contact with the over deeply indented, irregular line of steep bluffs that of very limited extent and are associated with a colored and has a cross fracture, the two are easily lying Laramie. In the Trinidad section the thin rise abruptly 500 feet above the gently rolling series of beds, altered by contact metamorphism, distinguished. The only fossil at all noticeable is sandstone layers of the lower zone rarely exceed country at their base. The mean elevation of the members of which can not be differentiated. the large oval, concentrically ridged shell, Ino- 3 inches in thickness, except near the base, where this platform is about 7500 feet, the western por In a later paragraph these will be described col ceramus deformis, characterized by the excessive there is a prominent bed of coarser sandstone tion being about 1000 feet higher than the eastern. lectively under the heading " Metamorphosed bulge of the ventral valve. The limestone itself,' from 3 to 5 feet thick. Toward the north bound It was originally an elevated plain or plateau, of Cretaceous." Of the unaltered sedimentary beds, however, consists largely of the skeletons of fora- ary the layers are appreciably thicker and the gentle inclination, but has been deeply scored by part belong to the Mesozoic (Cretaceous) and part miniferal organisms, readily seen in thin, transpar rock is of somewhat coarser texture. The erosion, and the present surface, rugged in the to the Cenozoic (Eocene and Neocene). ent sections under the microscope. The middle increased development northward is due to the extreme, is a succession of mesa-like ridges and and upper portions of the formation consist mainly expansion of the lower zone, which is from 70 to narrow valleys, the general character being CBETACEOUS PERIOD. of bluish or dove-colored shale, with thin bands 75 feet thick at Trinidad but about 90 feet thick emphasized by many perpendicular walls of rock The older Cretaceous formations of the region of limestone at intervals. There are three of these near the north line of the quadrangle. The upper (dikes) that occasionally rise to a height of 100 Dakota, Graneros, and Greenhorn are not rep bands from 1 to 3 feet thick in the Extent_ . of... the zone is about 80 feet thick throughout. It is feet above the surface and stretch for miles across resented, but they outcrop extensively in the upper 40 feet of the section, and one TimPas- characterized by the presence of Halymenites, the the country. In the northern two-thirds of the Elmoro quadrangle to the east and in the quad of these marks the top of the formation. The pitted, cylindrical stems of which are abundant. quadrangle the ridges have a rude radial arrange rangle to the west, and hence doubtless underlie resistance of the limestone to erosion renders the .Baculites in an imperfect state of preservation ment conforming to the drainage from the peaks. the entire district. Previously there had been a basal portion of the Timpas the most conspicuous are occasionally found in the lower zone. The In the southern third the principal ridges trend long period of land conditions, which of the marine Cretaceous beds, and its outcrop is, outcrop appears as a narrow, irregular line of toward the northeast, conforming to the drainage about the middle of the Cretaceous cretaceous more often than otherwise, marked by a limestone exposures extending in a southeast-northwest of the Raton Mountains, which culminate a few was succeeded by a long-continued, pro cliff. The upper contact is usually masked by direction across the northeastern part of the dis miles south of the boundary. found subsidence and an invasion by the ocean. soil in the limited area in the northeastern part trict. The Purgatory River is the main drainage The Dakota sandstone was deposited in the of the district where the exposures occur. Laramie formation. The marine Cretaceous channel. It traverses the southern portion of the brackish-water front of the advancing sea. As Apishapa formation. The total thickness of ended with the Trinidad. The conditions of the district from west to east and drains the shore line passed onward marine conditions the Apishapa approaches 500 feet. The lower succeeding Laramie epoch were shal- c dltlo Drainage. slightly more than one-half the quad were inaugurated, and with continued subsidence portion L for about 40 feet consists of Character_. low waters connected with the ocean. $SSngat rangle. The northern half is drained by a number the beds of the marine Cretaceous were succes dark-gray to blue-gray shales, followed ofnthextent Subsidence continued, but to a dimin- theLaramie- of small streams, tributaries of the Cuchara and sively deposited. by rotten shales of paper-like lamina- Apishapa> ishing extent, and the rates of subsidence and Apishapa, nearly all of which head in the Spanish Carlile formation. The lower marine Creta tion about 90 feet thick, which grade through sedimentation varied with respect to each other. Peaks. The two drainage systems are separated ceous beds of the region, represented by the blue sandy shale into calcareo-arenaceous shales. Thus, when the former exceeded the latter the from each other by a low east-west ridge that Graneros shale, resting upon the Dakota sand The latter become coarser and flag-like toward the water was probably deep enough to admit of the extends from the base of East Peak about two- stone, the Greenhorn limestone, or middle subdi middle of the formation and constitute about one- free action of tidal or other currents, and sandy thirds across the district a little north of the vision of the group, and the Carlile shale, or third of it.

Load more