330 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



certain that it forms a great treasure-house of geological knowledge, 

 from which many generations will draw fresh and interesting material 

 before its riches shall be exhausted. 



The enlightened measures adopted by our Government for the ex- 

 ploration of the public domain, the organization and thorough equip- 

 ment of the numerous surveying parties that have traversed the region 

 west of the Mississippi within the last twenty years, together with the 

 still more extensive explorations by private enterprise of our great 

 mining districts, have resulted in giving us materials from which an out- 

 line sketch can now be made that may be accepted in all its essential 

 particulars as accurate and worthy of confidence. 



It has happened to me to be connected with three of the Government 

 surveys to which I have referred, and to spend several years in travers- 

 ing the great area lying between the Columbia Biver and the Gulf of 

 Mexico. The observations which I have made on the geological structure 

 of our Western Territories supplement in a somewhat remarkable way 

 those made by Dr. Hayden, so that, taken together, our reports embody 

 the results of a reconnoissance stretching over nearly the whole of our 

 vast possessions west of the Mississippi. 



Our knowledge of the geology of this region has also been largely 

 increased by the no less important contributions of other explorers. 

 Among those who deserve most honorable mention in this connection 

 are Mr. George Gibbs, to whom we are indebted for most that we know 

 of the geology of Washington Territory ; to Professors W. P. Blake and 

 Thomas Antisell ; to Professor Whitney and the other members of the 

 California geological survey ; to Baron Bichthofen, the lamented Beniond, 

 Drs. Shiel, Wislizenus, and others. 



The results obtained by the last, largest, and best-organized party 

 which has been engaged in western explorations — that of Mr. Clarence 

 King — have not yet been given to the public ; but, from an examination 

 of some of the materials which are to compose the reports of this expe- 

 dition, I feel justified in saying that it will prove to be among the most 

 important of all the series of explorations of which it forms part; and 

 that the published results of this expedition will be not only an import- 

 ant contribution to science and our knowledge of our own country, but 

 a high honor to those by whom the work has been performed, and to the 

 Government, by which it was organized. 



Without going into details or citing the facts or authorities on which 

 our conclusions rest, I will in a few words give the generalities of the 

 geological and topographical structure of that poltion of our continent 

 which includes the peculiar features that are to be more specially the 

 subject of this paper. 



It is known to most persons that the general character of the topog- 

 raphy of the region west of the Mississippi has been given by three great 

 lines of elevation which traverse our territory from north to south: the 

 Bocky Mountain Belt, the Sierra Nevada, and the Coast Banges. Of 

 these the last is the most modern, and is composed, for the most part, 

 of miocene tertiary rocks. It forms a raised margin along the western 

 edge of the continent, and has produced that "iron-bound coast" de- 

 scribed by all those who have navigated that portion of the Pacific which 

 washes our shores. 



Parallel with the Coast Mountains lies a narrow trough, which, in 

 California, is traversed by the Sacramento and San Joachin Bivers, and 

 portions of it have received their names. Farther north this trough is 

 partially filled, and for some distance nearly obliterated by the encroach- 

 ment of the neighboring mountain ranges, but in Oregon and Washing- 



