Some of the most prevalant igneous features in the park are intrusive. Many times between 70 and 20 million years ago, the Big Bend region experienced great intrusions of magma. Many of the resulting intrusive features can be seen today as a result of erosional processes carrying away the overlying sedimentary rocks. Laccoliths, dikes, sills, and volcanic necks are many of the intrusive features that can be seen throughout the park, most of which can be viewed while driving on the park's highways. Dikes Dikes are vertical wall-like structures that form as a result of magma being injected into the fractures of rocks.
Dikes are discordant features.
This means that they cut through existing layers of rocks. Being intrusive, dikes crystallize below the ground. When the surrounding rock is eroded, dikes are exposed and often appear as dark walls of rock. Pictured to the left is a rhyolite dike that cuts through a bed of shale. On the road that leads west from Panther Junction, many dikes can be seen before you reach Tuff Canyon.