some of the youngest rocks in the park include the kahlitna terrane, which is a flysch sequence (a sedimentary rock sequence deposited in a marine environment during the early stages of mountain building) formed about 100 million years ago, during late cretaceous time. another rock sequence is the mckinley intrusive sequence, which includes denali. the cantwell volcanics include basalt and rhyolite flows, as well as ash deposits. an example can be seen at polychrome pass in the park.