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- Don i3 II. AFFECTED E~VIRONMENT This description sketches a general view of local, regional and statewide considerations. Chapters t and II of the Study Report present a detailed picture of the natural and human envtro~ents affected by the study. A. REGIOXAl. SETTI~C The Piedra River is the ~&t northeasterly tributary of the San Juan River (see Map 12). The San Juan River, the second largest tributary to the Colorado River, 1s located in the "Four Corners" area of Colorado, Utah, Arizona and New Mexico. The Piedra !l.asln produces approllt.ately 16 percent of the San Juan River flow. 11 In the a1"1d "Four Corners" area, water and the watersheds from which the streams originate are the geographic and economic lifeline. Ihe )11 square-miles dra1ned by the Piedra River above Colorado Highway 160 are primarily publl~ lands wirhio the San Juan National Forest. Approximately 16 percent of the 401,OOO-acre ~~=inuche ~ilderness is in the Piedra Valley. 8. PHYSICAL El>VIROSMENT Exposed geology of the Piedra River basin and planning unit ahow geologic processes from the Precambri4n period, forward in time to the Quarternary. The geologic history resulted in the land form and geologic values for which the river is being considered 45 a worthy addition to the National River system. !I Diverse geology and the various climatic cycles occurring during the geologic time scale have resulted in many different soils. A detailed lis ring of soil types is found in Appendix B-1. Although climate varies with elevation generally characteristic of the basin. 100daya. and exposure, ahort, cool summers and long winters are The aummer period (without frost) ranges from 48 to The Piedra River drains a productive watershed. Geologic Survey gage '349~ on the Piedra River near the Colorado Highway 160 bridge registered an annual average discharge of 223,900 acre-feet of water. 1/ Appendix C shows the discharge volumes for 1940-72. C. BIOLOGICAl. ESVIRO:''MENT n,e varied 50ils, exposure and elevation effects on climate have resulted in IS major vegeta- tive types or associations. When combined with landform in the Piedra valley, 48 combinations exist as a basis for ecological land units (ELU's): the river corridor contains 16 of the 48 ELU's (see Appendix B-II). The majority of the ELU's in the river ~orridor are unsuitable for development. nIOS", that are suitable are generally surrounded by others that are unsuit- able, resulting in little or no past development along &OSt of the river. The area dralned by the Piedra is well known for its big game mammal populations and associated sport hunting. ~e econnmically important species are the elk. mule deer, black bear and Bighorn sheep. The State Division of ~ildlife has identified 4) otber mammal., 17 species of reptiles and amphibians and 197 bird. [h,1t 1II8Y be found along the Piedra and itll tributary valley.. The Peregrine falcon, a bird On the Federal Endangered Species list, uses a portion of the study area for hunting, Fisheries in the Piedra river aystem are as diverse as any river system in southwestern Colorado. Currently, there are 20 known fish apeciea inhabiting the basin waters, the largest percentage being warm water fish in the Navajo Reaervoir. located below the river study area. 11 (;glorado 1,,;ater Conservation Board and USDA, Water and Related Land Resources San Juan Riv<;L Basin-Arizona. Colorado, ~ l'lexico and Utah, 197t., Type Four. Cooperative Study, pp. 1-1 - lIt-I. II Larsen. Esper S. alld "''hit"""n Cross, Geology and Petrolo!':v ~ the San Ju.an Region Southwestern Colorado, 19~6. USDI-Geological Survey, Professional Paper 158. pp. 1-11. 11 ~SDI-Geologi~al Survey, ~ater Resources Dsta For Colorado. Part I. Surface ~ater Records. 197). 1-6 , .., I I f