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<br />PURGATOffiE (PICKET. WIRE) RIVER,COLO.
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<br />7
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<br />6. Topografhy.-The relief in Purgatoire Basin varic~ OVcr 10,000
<br />fect in clevatlOn from its headwaters to its mouth. On the western
<br />boundary along Culebra Range, Purgatory, Oulebra, and Trinchera
<br />Peaks exceed 14,000 feet in elevation. The northern drainage divide
<br />from Trinchera Pcak desccnds about 7,500 feet in 30 milcs to the
<br />vicinity of Ludlow, 0010" along thc front range. From this loeation
<br />tho watoi'shcd is located in tho plains rogion. Thc southcrn water.
<br />shcd is rough.ly parallcl t? the Oolorado,.N ew Mexico State line from
<br />Sangre de OrIS to Mountams eastcrly. to Mesa De .Maya, a dIstance of
<br />about 80 miles. The goneral elevatIOns along thIS part of the ,divide
<br />are 13;000 at thc western end, 8;000 feet in the vicinity of the head'.
<br />w!J,ters 'of Lorencito and Long Oanyons, and 9,500 feet on Raton Mesa'
<br />in the headwaters of RatonOanyon, south of- Trinidad, 0610" From
<br />the maximum elevation on Raton Mesa, the elevation decrcases to
<br />6 500 feet in about 10 miles. The remainder of the Southern divide
<br />i~ locatod in the plains area. The drainage basin west of Trinidad
<br />Colo., is rugged and mountainous. East of Trinidad the plains which,
<br />have bcen dissectod arechara<:te.riz~d by plateaus, mesas, and deep
<br />canyons. General topography IS Indloated 01} map No.1, appendix A:
<br />, 7. From the confluence of North and M,ddle Forks ta Arkans!lS
<br />River, ~urgatoire .River flows thraugh fo~r ,distinct .sections: ,(1) the
<br />1notlntamous. sectIOn t1pst~eam from Trlll~dad (mIle 186 to 157);
<br />(2) an allUVIal valley sectIOn about 35 Im!es long below Trinidad
<br />(mile 157 to 122) ;(3) a rugged can:fon sectIOn abput 105 miles long
<br />(mile 122 to 17); (4) a second alluvlltl valley sectIOn about 17 miles
<br />long (mile 17 to 0): The valley in the mountainous section up,
<br />stream from Trinidad is narrow, varying in width from a few hundred
<br />feet to about one,fourth mile. ' ~etween. Trinidad and the canyon
<br />scc.tw,!l, the valley reaches a maxImum WIdth of about thrce'fo\1rths
<br />mile.' Throughout most of the canyon section, precipitous walls con.
<br />fine the rIver. Between the lower end of the canyon and the river
<br />meuth, the lower yalley s?ction reaches a ma,!,imu~ width of about 1
<br />mile, TopographlO detltlls of the PurgatoIre RIver VaHey from
<br />mile 163 to mile 122 are shown on maps Nos. 2 to 7,' apPendix A.
<br />' 8. Geololly.-'-The geology of the watershed is eomplex due to
<br />rapidly changing topegraphy. In the upper headwater reaches the
<br />streams flow oyer suee~ssively younger strata which dip steeply to
<br />the east and crop out m north,south belts. The strata consists of.
<br />poorly consolidated red san~stones and shales interbedded with thin
<br />I limestone of the Pennsylvaman, and a serIes of sandstenes and shales
<br />interbedded with limestones and coals of the Jurassic and Oretaceous
<br />periods. . From about longitude .1050, west .to the vicinity- of Sopris
<br />Colo. (mIl,e 162), the rIver and Its trIbut",!,les flow OVer IUterbedded
<br />sandstones, shales, and coals of early Tertlltry period (Raton forma-.
<br />tion), ;North of the river and west of the town of Bonparbo, Colo.,
<br />near mIle 170, these strata are overlam by a maSSIve sandstone
<br />cp'oison Oan.v:o~ .formation). Seyeral igneous dikes .are exposed in
<br />thIS gcneral vI,Clmty. From Soprls to the Arkansas R,ver Valley, the
<br />bcdrocks conSIst of sa.ndstones a.nd shalesmterbedded with limestone
<br />and coals of the r:c~lan, JurassIc, and Cretaccous periods. Between
<br />Sopns and the VlCllllty of mile 65, the strata dip west and become
<br />successively older towards the mouth of the river. Downstream from
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<br />11'hCSf> maps arc not printed.
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