(above right) Sketch redrawn by Abe Lillibridge, from original by the Ferdinand V. Hayden expedition of the U.S. Geological Survey. View looks north and east across the Portneuf River from near Blackrock toward the Pocatello Range, the city of Inkom, Rapid Creek, and the Portneuf Range on the right. Note: in the caption to the illustration, "do" means "same as above." Hayden failed to recognize that the limestones on the east end of the canyon (cambrian Elkhead Limestone) are younger than those near Blackrock on the west end (late Proterozoic Blackrock Canyon Limestone). We now know the mountains to be made up mostly of the Late Proterozoic and Cambrian Brigham Group. The Basalt of Portneuf Valley in the foreground is about 600,000 years old. Click on image for a larger view.

(below) Inkom-Portnuef Narrows Map.