The purpose of this study is to determine the regional structure and tectonic history of the Absaroka Volcanic Field of northwestern Wyoming including the Absaroka Mountains and parts of Yellowstone National Park (Fig. 1). The Tertiary (probably Eocene) volcanic rocks of this field attain a thickness of more than 6500 feet.
The specific problems are as follows :
Types of the volcanic rocks, their sequence, and the pre-volcanic topography on which they rest.
The origin of the volcanic rocks.
The relation of the volcanic rocks to the basement rocks and to the major structural features such as Heart Mountain and other thrust masses.
The writer made a detailed study of a small, but representative area of the Absaroka Volcanic Field during the summers of 1930 and 1931, and many reconnaissance trips throughout the entire field in 1932 . . .