Often a resistant layer, like sandstone, at the top protects less resistant layers below from erosion. Buttes are common in the American southwest. About 100 MYA this area was covered by an transgressive-regressive sea which deposited alternating layers of limestone. Some layers are more resistant than others. Harder deposits produce steeper, often cliff-like terrain, whereas softer layers produce slopes.
Exfoliation domes are the result of erosion and uplift exposing batholiths.
Batholiths are igneous intrusions formed beneath the earth's surface. As erosion removes the overlying strata the batholith expands and develops curved fractures. Upon exposure these fractures caused rock to break off in slabs known as exfoliation sheets. Stone Mountain, Georgia and Looking Glass Rock in North Carolina are other examples of this type of feature. Lava flows are sometimes associated with these eruptions.