COLORADO RIVER BASIN 
289 
OUTSTANDING GEOLOGICAL FEATURES OF 
COLORADO RIVER BASIN ^ 
By Dr. Frederick J. Pack 
Utah State University 
The Colorado River Basin comprising parts of Wyoming, Colo¬ 
rado, Utah, Arizona, New Mexico, Nevada, California and old 
Mexico, constitutes an area of nearly a quarter of a million of 
square miles. Only 2,000 square miles of the total area lie outside 
of the territory of the United States. Quite properly, much of 
the discussion should no doubt relate more or less directly to the 
Grand Canyon of the Colorado and its immediately contributing 
territory, but attention will be directed mainly to the Plateau 
country of northern Arizona and southern and southeastern Utah. 
Although the country comprising this area alYords evidence of 
having been part of a great continent far back near the beginning 
of geological time, the factors which immediately gave rise to the 
Basin in its present form, are of much more recent date. The 
topographical features out of which the modern Colorado River 
Basin was evolved seemingly had their origin in the development 
of Cretacic geology. 
All are familiar with the fact that during this Cretacic Period 
% 
a great interior sea extended in a general direction through the 
Rocky Mountain region from Texas to Alaska. Details of the 
geography were, of course, repeatedly modified; yet, in the 
main, the general outlines were more or less constant. Near the 
close of Cretacic time, however, a mountain-building movement 
occurred which transformed the entire geography of the region. 
1 Address, in Symposium on the “Problems of the Colorado River,” delivered before 
the American Association for the Advancement of Science at the Salt Lake City 
Meeting, 1922. 
