EXTRACTS FROM THE T 76 REPORT 
HAYDEN SURVEY OF THE TERRITORIES FOR 1876 
Work of W. E. Holmes, -ygy 
in charge of Mr. Wilson 
"In company with the triangulation party,/Mr. Holmes made a 
hurried trip through Colorado, touching also portions of New Mexico 
and Utah. He was unable to pay much attention to detailed work, but 
had an excellent opportunity of taking a general view of the two 
great plain belts that lie, the one along the east, the other along 
the west base of the Rocky Mountains. For nearly two thousand miles 
travel he had constantly in view the Cretaceous and Tertiary forma¬ 
tions, among which are involved some of the most interesting geologi¬ 
cal questions. He observed, among other things, the great persist¬ 
ency of the various groups of rocks throughout the east, west, and 
north, and especially in the west; that from Northern New Mexico to 
! Southwest Wyoming the various members of the Cretaceous lie in al- 
imost unbroken belts. 
Between the east and the west there is only one great incongru¬ 
ity. Along the east base of the mountains the Upper Cretaceous 
rocks, including Nos. 4 and 5, are almost wanting, consisting at 
most of a few hundred feet of shales and laminated sandstones. Along 
the west base this group becomes a prominent and important topograph¬ 
ical as well as geological feature. In the southwest, where it forms 
the "Mesa Verde" and the cap of the Dolores Plateau, it comprises up¬ 
ward of two thousand feet of coal-bearing strata, chiefly sandstone, 
while in the north it reaches a thickness of 5,500 feet, and forms 
the gigantic "hog-back" of the Grand River Valley. 
While in the southwest he visited, the Sierra Aba jo, a small 
group of mountains, which lie in Eastern Utah, and found, as he had 
previously surmised, that the structure was identica 1 wi th that of the 
four other isolated groups that lie in the same region. A mass of 
trachyte has been forced up through fissures in the sedimentary 
rocks, and now rests chiefly upon the sandstones and shales of the 
Lower Cretaceous. There is a considerable amount of arching of the 
sedimentary rocks, caused probably by the intrusion of wedge-like 
sheets of trachyte, while the broken edges of the beds are frequently, 
but abruptly, pressed up, as if by the upward or lateral pressure of 
the rising mass. He was able to make many additional observations 
on the geology of the San Juan region, and secured much valuable 
material for the coloring of the final map. 
He states that the northern limit of ancient cliff-builders in 
Colorado and Eastern Utah is hardly above latitude 37° 45* 
(Page XV) 
Holmes 1 report on the Geology of the Sierra Abajo and West San 
Miguel Mountains occupies pages 189-196 with illustrations. 
