Date of Award:


Document Type:


Degree Name:

Master of Science (MS)




Donald R. Olsen


The tuffs and limestones of the Tertiary Salt Lake Formation in northeastern Cache Valley, Franklin County, Idaho, are intruded by basic and intermediate igneous dikes and sills. The Tertiary intrusives are exposed in an area 10 miles long and 2 miles wide between Bear River and Maple Creek in the foothills of the Bear River Range east of Preston, Idaho. They trend north-northwest. The intrusives are mostly diabase but include a small body of syenodiorite and several small andesite dikes. The intrusives seem to be emplaced along early Basin and Range faults. They are limited to the Cache Valley Member of the Salt Lake Formation and pre-date the Mink Creek Member of the Salt Lake Formation in the mapped area. The probable age of the intrusive activity is late Pliocene. Because the igneous rocks are well exposed on both sides of the Cub River valley, they will be referred to as the Cub River Diabase. The Cub River Diabase could represent a southward extension of the early igneous activity in the Snake River Plain.



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