ABSTRACT
The most prominent topographic feature in southeastern Colorado is a double-capped butte known as Two Buttes which rises abruptly 400 feet above the surrounding Tertiary plains. The butte is capped by sandstone of probable Triassic (possible Jurassic) age dipping 10° W.-NW.
Immediately southeast of the butte an igneous mass is exposed with an area of more than one-quarter of a square mile. The igneous rock appears to be andesite porphyry. It is locally in contact with a ledge of limestone and dolomite (Alibates) in which it has induced slight contact metamorphism. The porphyry has obviously pushed up the resistant dolomite and overlying beds and has spread out somewhat so as to form a laccolith. The resulting closure in the overlying sediments is about 800 feet. The age of the intrusion is probably late Miocene.
Slightly more than 900 feet of sediments is exposed within the small area of the Two Buttes dome. These sediments range from Permian (Whitehorse) through Mesozoic to Cenozoic. The geographic position of Two Buttes makes the exposed section valuable both to Mid-Continent and to Rocky Mountain geologists, serving as it does to link stratigraphic markers from both regions.
