Big Bend National Park

Trail Marker 24

This Pinyon Pine tree has in the grasp of its roots a jumble of rock fragments. The tree's roots extend into cracks in the rock surface on which it's growing. As time passes, the growing roots expand cracks in the rock, forcing rock fragments to break away from the main rock. This is a form of biological weathering.

The photograph to the right is of Desert Varnish on tuff; the dime in the center of the photo is for scale.. Tuff is a rock formed from the lithification of volcanic ash and pyroclastics (lava that's been thrown into the air). Because it is of volcanic origin, tuff is very mineral-rich. As water seeps through tuff, the water picks up and dissolves many minerals. Once the mineral laden water reaches the rock surface, some of the minerals get trapped on the dusty rock surface by bacteria colonies. Desert Varnish is formed over a long period of time by bacterial oxidation of deposited iron and manganese.

Near Trail Marker 26

The bright green rock in the photograph at left is olivine. Olivine is a silicate rock rich in iron and magnesium that forms when magma cools below ground. Although the olivine pictured here is bright green, its color can range from green to black. In its massive form (as it is here), olivine has a glossy surface and a concave fracture. Olivine can also form as a granular, crystalline mineral.

Trail Marker 30

Lost Mine Peak is visible from Trail Marker 30. The peak's elevation is 7,650 feet. Lost Mine Peak is made of rhyolite, an extrusive form of granite. The top layer of rock on the peak is from a great lava flow that happened in the park more than 30 million years ago.

Trail Marker 31

During the Ice Age, Ponderosa Pines were a common sight in the southwestern region of North America. As the continents drifted and the regional climate became hotter and drier, only the Ponderosa Pines at high elevations survived. Here in the Big Bend, the only surviving stands of Ponderosas are on the eastern side of the Chisos Basin, visible from the Lost Mine Trail.