Fine-grained volcanic ash from volcanoes west and northwest of the Teton area was periodically deposited in the quiet shallow water of the Western Interior Seaway throughout Cretaceous time. Ash deposited in this manner was later altered to bentonite; a type of clay used in the foundry industry and as a component of oil well drilling mud. Elk and deer in Jackson Hole use exposures of bentonite as a (bitter) salt lick. Bentonite swells when wet, which causes landslides that sometimes block access roads into Jackson Hole.