GEOGEAPHIC CHARACTERISTICS OF THE THREE PROVINCES. 7 



the latter were in large part derived from the former. The Basin Province 

 was the dry land that fed the sea and great lakes of the Plateau Province 

 through a long period, while many groups, each thousands of feet in thick- 

 ness, were deposited. 



Thus, for convenience of geological discussion, I speak of three great 

 geological provinces the Park Province, the Plateau Province, and the 

 Basin Province in order from east to west. 



The area included in these three provinces lies east of the Sierra Ne- 

 vada and west of the Great Plains. In a general way the northern boundary 

 is marked by the North Platte, with its proper upper continuation the Sweet- 

 water River whose minute upper ramifications interlock with those of the 

 Shoshoni River, which latter is a continuation of the northern boundary 

 until it is crossed by the forty-third parallel of north latitude. When the 

 region along the middle course of the Shoshoni River is more thoroughly 

 studied, the Basin Range System may be carried much farther north than 

 we are warranted in doing with our present knowledge; but I am inclined 

 to the opinion, from the fragments of geological description which we have 

 from that country, that another distinctly marked group will eventually be 

 recognized here, having for one of its characteristics a great development 

 of eruptive rocks. The southern boundary of the three provinces I am not 

 able to clearly define. 



It may be well to state somewhat more categorically the characteristics, 

 geographic and geological, on which I propose to divide this great area into 

 three provinces. 



GEOGRAPHIC CHARACTERISTICS OF THE THREE PROVINCES. 



The Basin Ranges are short, more or less distinct north and south 

 ridges separated by desert valleys which reveal broad stretches of sub- 

 aerial gravels concealing the underlying formations. The general drainage 

 is to interior salt lakes and sinks, but in the northeast corner there is a 

 limited district drained by some small tributaries of the Shoshoni, and in 

 the southeast there is a small district drained by the Rio Virgen into the 

 Colorado River of the West. 



