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<br />" <br /> <br />~ <br /> <br />. <br /> <br />Carboniferous, Jurassic, and Cret~ceous periods rise to ~o surfnco as <br /> <br />hogback ridgos. ES3t. of tl'l8se ricigo3 the fl&t-lying deposits of Tsrt!.ary <br />sgo occur. Alpine glaciation ooctlrrec. in the western portion of tho <br />watershed during the Pleistocene age. <br />Soils of ~~e ~ntershed are derived princip&lly from Granite &nd <br />gneics. Tho soils derived from ,the fomer STe gravelly sundy lonms, <br /> <br />verf ?or.1eable, and oc~~r for tho most part on steep slopes amid fre~tlent <br /> <br />rock outcrops and er-ode rapidly when the cover of either forest or grass <br /> <br /> <br />is disturbed rae.terially. The soils derived fro:! gneiss .f...re permeable, <br /> <br /> <br />gra.....Blly fine sendy loe.~s to loaIn3 high in organic matter. Large numbers <br /> <br /> <br />of sngul1'.r e;ravel fr"gments several inches in diameter occur in all soils <br /> <br />2~d often foro an erosion pavement Which tends to reduct. bo~~ run-off and <br /> <br />eroaion. <br /> <br />The Bear Creek drainage is characterized by steep narrow valleys <br /> <br /> <br />until it suddenly emerges on the pleins near its conz'1uence ~ith the <br /> <br /> <br />Sou~':\ Platte River. The gradient of the tributary streEl1lS rising in <br /> <br /> <br />~he mountains u~~ally exceeds 200 feet per aile and gradients in excess <br /> <br />of 500 feet pOl' mile are common. <br /> <br /> <br />Run-off, aggravated by excessive grazing, highway construction, and <br /> <br /> <br />forest fires has caused severe chF~nel cutting in the deep valley soils <br /> <br /> <br />along tribuk,ry strea:as in the eastern portion of t..':\e watershed. In <br /> <br /> <br />addi tion, the crowding of normal stream channels by rOllds and by tha <br /> <br /> <br />construction of buildings as in the reach bet~cen Evergreen and Morrison <br /> <br /> <br />has concentrated flood flows and increased their powers of destruction. <br /> <br /> <br />Upstream from Evergreen where no serious destr~ction of plant CO,er and <br /> <br />soil has occurred, the channels are adjusted in size and ca~acity to, <br /> <br />- 2 - <br /> <br />. <br /> <br />