Washington, D. C., December, 1855. 
Sir: I herewith submit some observations upon the geology of the region explored by 
Captain Pope, near the 32d parallel, in 1854, based upon the collection of rocks and fossils 
which were placed in my hands by you for description. 
This collection of rocks, taken from various points along the route, is very interesting and 
complete, and doubtless presents a fair view of the mineral characters of the formations. A 
list of the collection, and descriptions of the most important specimens, will he found in this 
report. The fossils, although not numerous, are from interesting localities ; hut there are no 
species which have not been previously described and figured. 
I have made free use of the descriptions of the main features of the country contained in 
Captain Pope’s report; and in the absence of all geological sections, I have been guided by 
the topographical and general descriptions in assigning the boundaries of the different 
formations. 
Respectfully, yours, 
WILLIAM P. BLAKE, 
Geologist of the Office of the U. S. Pacific 
Railroad Explorations and Surveys. 
Captain A. A. Humphreys, 
U. S. Topographical Engineers , in charge of the 
Office of U. S. Pacific Railroad Explorations and Surveys. 
