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<br />the mark of °Uaconformity" oa eeation between the ktancos Shale• end San <br />-" °°- - del, masers that the taro forsa[ttions differ in their bedding. The ^aen iiii{'Uel <br />' _ ~ ps to theeast and the underl ! sedimen <br />- - y nS terry bads dip to the vest. This fa <br />it sheen ~- plwtograph herewith narked "Unconfornity P1. T." This photo vac <br />ea from a point ott the third bench above Piusdora looking south aoroae the San <br />'yuel River. By tracinS out the lines of strata near bottom of picture it will <br />ease tl^.at they gradually approach each ot}ser liY.e a IetterL but with a Seas <br />In the introduction to the report of IYtr. Gross he aayss °The term San Snan <br />ginr., or simply°the San Jusn,° used with variable mesuing by early explorers, <br />r:eturally with in!eTlnite iimitatioa duris~ the period of eettlec"ent~ 1s nov <br />~" ire reaerally applied to a large tract of mountainous country in South-scot®rn <br />olor~o~ together aaith an undefined zone of lover country bordering it on the <br />._..,. <br />rth, vest and south. The Coatinaatel e~ivide traverses thin country in a great <br />>q. Tre principal Part of the district ie c deeply scored volcanic plateau, <br />square <br />re Lima 3000 Hiles f.n extent, drained on the north try the tributaries of Lhe <br />;; <br />' ~ °~ ^"iSOA P.fYer, On tt:e SFeat ay SliOap OI titfT JOiOI'e3 RFIa ~1 YJijjli0i nivo""ro, va vi{v <br />{tl: by nur,eroue branches of the San Juan, and an the east by the Rio Grarxie. <br />1 but the latter 8raina:;e firsts it maq to the Gulf of Califortsia through the <br />lorado River." ~x x : z x <br />- °27ie Geological history of the San Juea region is too complex and as yet <br />o ir~,erfectly knosra to admit of even an outline stritement of eatistactory acour- <br />,_ ~ y. 1'~e pro-Tertiary surface of the satire region mac completely buried by the <br />lcanic farmatios:s which aov cover the nciin area, ntd, mhils. erosion }use again <br />used aorxi of tY:t older rooks on all aides at the voloanio complex and even in <br />.e of the iatelior valleye~ the reaorwoiseaa~e obeervationa of the Hayden aruf <br />:err surv$ys ooze far too meager, axtti the present survey has thus far oovered too <br />~~ <br />i', <br />-`' i <br />~i <br />,, <br />'~' <br />~1 <br />i <br />ij <br />ti <br />1 <br />