Yampa Canyon in the Uinta Mountains Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-1 Yampa Canyon in the Uinta Mountains Colorado By JULIAN D. SEARS SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-1 A study of some unusual features and the possible origin and development of the canyon UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS Page Page Abstract_ ________________________________________ 1-1 Observed features Continued Introduction _______________________________________ 3 Lower section of Yampa Canyon Continued Purpose of the report-_ __________________________ 3 Topography of canyon walls _________________ 1-12 Usage of two terms_-_--------__________________ 3 Topography of adjoining uplands_____________ 13 Sources of information_________________________ 4 South of canyon._______________________ 13 Earlier investigations-_____________________ 4 North of canyon________________________ 13 Newer sources__-_------_-__________________ 4 Geology ___________________________________ 14 Geologic map in present report _______________ 4 Warm Springs scar an exception_____________ 14 Acknowledgments. ____ __________________________ 5 Suggested explanation of the features __________________ 15 Observed features...-___--_-_---__-____-____________ 5 Concepts of 1922-23___.________-____-__----__ 15 Yampa Canyon as a whole_______________________ 5 Original extent and thickness of Browns Park forma- Statistical details___---_-__________-________ 5 tion________________-__________-_---_-----___ 16 Relation to Yampa fault and other faults _______ 5 Area of maximum thickness-_________________ 17 Yampa fault___________________________ 5 Browns Park formation in Lily Park-_________ 17 Red Rock fault_______________________ 5 Possible Browns Park material on Douglas Mitten Park fault_____________________ 6 Mountain. _ ____________________________ 17 Graben between Red Rock and Mitten Browns Park formation near Elk Springs. _____ 18 Park faults.__-____-_-_______________ 6 Nearness of Browns Park formation to east end Three-part division of canyon ________________ 6 of Yampa Canyon._______________________ 19 Upper section of Yampa Canyon. ________________ 6 Possible Browns Park material on Blue Moun­ Middle section of Yampa Canyon_________________ 7 tain. ____________________________________ 19 River pattern and direction._________________ 7 Possible Browns Park material on Harpers Topography of canyon walls.________________ 7 Corner._-________________--____-_-_-___- 19 South wall._---_-_-__--___-____________ 7 Possible Browns Park material west of Lodore North wall--_--__----_-_-_---______--_- 7 Canyon___. ______________________________ 19 Topography of adjoining uplands _____________ 8 Summary_ _ _______________________________ 20 South of canyon._______________________ 8 Possible development of the canyon a chronological North of canyon_. ______________________ 8 outline ______________________________________ 20 Geology ___--_-----_-_--___________________ 9 First step_____________________-___-_-_-_-_- 20 South of river_________ _________________ 9 Second step._________________----__--___--_ 20 North of river_________________________ 9 Third step.._.._._._-__________________ 21 Meander-migration scars.__________________ 9 Fourth step_______-__-________-_-_-_-___-_- 22 Anderson Hole scar.____________________ 10 Fifth step. _____________________-__.__ 24 Tepee Hole scar________________________ 10 Sixth step______________________--_----___ 25 Browns Hole scar_______________________ 11 River development in Morgan formation.- 26 Bower Draw scar__-___-________________ 11 River development in Weber sandstone. __ 27 Five Springs Draw scar____-__-__________ 11 Seventh step.______________________________ 28 "Half-turn district" an exception. ___________ 11 Effect of Mitten Park and Red Rock faults ________ 28 Lower section of Yampa Canyon________________ 12 Selected bibliography________________________________ 30 River pattern and direction__________________ 12 Index.____________________________---________--- 33 ILLUSTRATIONS PLATE 1. Geologic map of Yampa Canyon and vicinity, Uinta Mountains, Colorado___-_______________---------_ In pocket Page FIGURE 1. Entrance to Yampa Canyon___________________________________________________________________________ 1-6 2. Upper section of Yampa Canyon________________________________________________________________________ 7 3. Sharpened spur between Tepee Hole (second) and Browns Hole Cthird) scars_________________-_-_-_-_---___- 11 4. "Tiger Wall" in lower section of Yampa Canyon_______________________________________________________ 12 5. Lower section of Yampa Canyon. Intricate meanders in Weber sandstone___________________---_-_---_-____ 13 6. Warm Springs (sixth) scar____________________________________________________________________________ 15 7. Map of eastern Uinta Mountains and vicinity, showing part of the mapped Browns Park formation____________ 18 8. Hypothetical course of Yampa River between points B and C when cutting through Browns Park formation.___ 25 9. Possible former high-level channel of lower part of Yampa River. __________________________________________ 30 m SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY YAMPA CANYON IN THE UINTA MOUNTAINS, COLORADO By JULIAN D. SEARS ABSTRACT Yampa Canyon, northwest Colorado, was incised in the south­ curve of the river. Its intersection with the adjoining upland ern flank of the Uinta Mountain arch by Yampa River. is sharp. Modern topographic and geologic maps and aerial photo­ Except in the "half-turn district," the north wall is wider, graphs of the canyon and vicinity have disclosed unusual fea­ less steep, and of irregular shape. It consists chiefly of ad­ tures, among which are: natural division of the canyon into joining scallop-shaped erosion surfaces or scars. Southward, three sections; marked change in river pattern from the mid­ however, these moderately sloping surfaces end in a steeper dle to the lower section; in the middle section, radical differ­ slope down to the river, making a break in slope convex up­ ences in topography and geology on its two sides; also in the ward. middle section, but only north of the river, several scallop- The Untermanns' geologic map of Dinosaur National Monu­ shaped erosion surfaces or scars partly rimmed by cliffs and ment shows conspicuously that the south wall serves as a with moderately sloping floors; in the lower section, still dif­ formation boundary. The upper part of the south wall and ferent topography and general absence of scars; geographic the upland immediately south of it consist of the Weber sand­ and geologic relations between Yampa River and the Yampa, stone, about 900 feet thick, which is loosely cemented and Red Rock, and Mitten Park faults. highly jointed. The lower part of the south wall, the north The observed features give further clues to the origin and wall, and the adjoining belt of upland expose beds of the next development of the canyons and anomalous courses of Green older Morgan formation (except in the "half-turn district" and Yampa Rivers across the Uinta Mountains. where the Weber sandstone remains). The Morgan is about South of and crudely paralleling Yampa Canyon is the 1,200 feet thick, of sandstone and limestone; the lower part Yampa fault and its branch the Red Rock fault, both with is more resistant to erosion. downthrow on the north. Apparently the Red Rock fault ends The hypothesis is advanced that the scallops north of the at the Mitten Park fault, which has downthrow on the south­ river are "meander-migration scars" formed by the progres­ east. Thus the Yampa River joins the Green within a west­ sive downdip (southward) migration and lowering of early ward-pointing triangular graben between these two faults. meanders of Yampa River, by an unusual form of homoclinal The upper section of Yampa Canyon, nearly 2 miles long, shifting on more resistant beds in the lower part of the Mor­ cuts stratigraphically downward through the Weber sandstone gan formation. In the middle section of the canyon five such and Morgan formation, both of Pennsylvanian age, at right scars are distinguished; because they differ somewhat from angles to the northeast strike and against the southeast dip each other they are named and separately described. of about 12° that mark the end of the Uinta Mountain arch. The lower section of the canyon differs markedly from the The river's course is fairly simple, and topography and geology middle section in several ways, the most striking and signifi­ on the two sides are similar. cant of which are: (a) A notable change in river pattern. The middle section of the canyon is nearly 20 miles long; Meanders are more numerous and more intricately curved, its fall is 333 feet, an average of about 17 feet per mile. (b) Topography of canyon walls and of adjoining uplands Near the point where the middle section begins, the strike of generally different from the two types in the middle section. the beds swings sharply to a direction north of west, parallel Cross profiles are asymmetric but alternating because of inter­ to the axis of the arch; the dip is predominantly 6° SW. locking spurs with slipoff slopes, (c) An abrupt change in the This changed structure extends westward to and beyond the relation