GEOLOGICAL REPORT ON THE GRAND RIVER DISTRICT. 



CHAPTER I. 



GENEEAL INTEODUCTIO!^. 



The area assigned to the Grand River Division for 1876 was divided 

 into two parts. First was a district of about 1,000 square miles south 

 of the Sierra la Sal, between the Dolores and San Miguel Rivers, and 

 extending south as far as the parallel of 38°. The larger portion of the 

 area, consisting of about 3,000 square miles, lies north of Grand River, 

 extending from the river as a southern line, northward to the parallel of 

 390 30', bounded on the east by the meridian of 108<^, and on the west 

 by 1090 30'. 



Sedimentary formations prevail in both districts. The area (area A) 

 south of the Sierra la Sal is the portion not completed in 1875, on ac- 

 count of the difficulty with the Indians, and it is the area first worked in 

 1876, nine days being devoted to it. A general view (Fig. 1, Plate X), 

 obtained from the summit of Lone Cone, shows it to be plateau-like in 

 general, cut by deep gorges or canons toward the east, and rendered 

 somewhat irregular toward the west by several broad folds. Near 

 Lone Cone Mountain the country is somewhat hilly, and in places mesa- 

 like. Here the Cretaceous shales (Middle Cretaceous) are seen resting 

 on the Dakota group, which in general forms the floor of the plateau. 

 The streams cut through the Dakota group exposing the Jurassic shales, 

 especially toward the north, and as we follow the streams we find them 

 cutting deeper and deeper, until the Red Beds (Trias?) appear beneath 

 the Jurassic. West of the San Miguel Plateau, beyond Naturita Creek, 

 the Dakota sandstones rise in a fold, the axis of which is northwest 

 and southeast. Toward the northwest this fold is marked by the Par- 

 adox Valley, which appears to occupy its axis. Beyond Paradox Val- 

 ley is the Basin Plateau. This is a gentle synclinal basin ; for the 

 strata on the west side of Paradox Valley dip gently to the southwest 

 and, beyond the centre of the basin, rise again gently to the edge of 

 the bluffs forming the eastern or northeastern wall of Gypsum Valley, 

 which is similar to Paradox Valley. Between Gypsum Valley and the 

 Dolores River is another synclinal basin, the sides of which dip south- 

 west and northeast. At the northwestern end there is a dip to the 

 southeast, which gives a saucer-like shape to the valley. From this 

 fact we called it Saucer Valley. Around the northwestern end or rim 

 of this valley the Dolores flows in a canon, emerging from it into Gyp- 

 sum Valley. Southwest of the Dolores the country rises into the north- 

 ern border of the Sage Plain. In working up this area we took the 

 following routes: From the crossing of the S; n Miguel we travelled 

 northwestwardly along Naturita Creek, reach'- the San Miguel again 



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