Canyon County is entirely on the Snake River Plain, between the Snake River on the south and the foothills of the central Idaho Mountains on the north. Much of the county is underlain by Quaternary alluvium of the Boise River and Pleistocene gravel from glacial outwash. This gravel forms high benches above the Boise River.
Several normal faults run northwest through the county, parallel with
the northern boundary of the western Snake River Plain. Miocene lake beds
make up the foothills on the northern boundary of the county.
Quaternary basalt covers the southeastern section of the county. Miocene and Pliocene lake beds of the Glenns Ferry and Chalk Hills formation are found on the bluffs north of the Snake River.
Also see the report by Othberg and Gillerman on the geology of the Boise Valley.
P.K. Link, 10/02
Rocks Rails and Trails: pages
Challis Volcanic Group & Intrusive Rocks
References on Idaho Geology
Click here for a printable version of this map.