TO JUNCTION OF GKAND AND GKEEN 1UVERS. 



General section of the Valley of the Colorado. 



Finding it impossible to pass down in the vicinity of the Colorado to its junction 

 with the San Juan, we were compelled to retrace our steps, and again ascending to 

 the Sage-plain, crossed southwardly over its western extremity, along the eastern base 

 of the Sierra Abajo, to the San Juan Valley. This part of our route afforded us little 

 that was new in any department, and need not, therefore, long detain its. We found 

 the structure of this portion of the Sage-plain precisely like that before passed over. 

 The Lower Cretaceous sandstones everywhere form the surface-rock, except where 

 covered with the overlying shales. The fossils of these shale-beds are often thickly 

 scattered over the surface, as in many localities enumerated on the preceding pages. 

 The plateau is here, as farther eastward, more or less broken by the canons of the 

 draining streams. These head in the Sierra Abajo and progressively deepen until they 

 terminate in the eroded valley of the San Juan. At various points along this part of 

 our route we saw ruins of ancient buildings, similar in character to those on the 

 Dolores ; and fragments of broken pottery, an equally characteristic record of the 

 Pueblo race, were everywhere met with. 



Sierra Abajo. Our near approach to the Sierra Abajo, while skirting its northern 

 and eastern bases, gave us a better knowledge of its extent and structure than we had 

 before obtained. The impressions we then received of it are given in the following 

 extract from my notes: "August 30, Camp 31, Mormon Spring. Our last camp was 



