Question

One of the main attractions at this park is a forest of large petrified trees. These trees were preserved by being replaced with silica from ash layers within the Triassic (Mesozoic) sandstones. Based on the geologic history and features of the area, which of the following statements about these sedimentary rocks is TRUE? a. The clastic sand that forms these rocks was weathered and eroded from the Appalachian Mountains. b. The ash was produced from volcanoes associated with the Yellowstone Hotspot. c. The clastic sand that forms these rocks was weathered and eroded from the Rocky Mountains. d. The clastic sand that forms these rocks was weathered and eroded from the Sierra Nevada Mountains.

Answer 1

Answer: d. The clastic sand that forms these rocks was weathered and eroded from the Sierra Nevada Mountains.

Explanation: Petrified Forest National Park is known for its fossils, especially of fallen trees that lived in the Late Triassic Epoch of the Mesozoic era, about 225 million years ago. During this period, the region that is now the park was near the equator on the southwestern edge of the supercontinent Pangaea, and its climate was humid and sub-tropical

The older (lower) layers of the formation consist of fluvial and lacustrine (lake-related) deposits of silt, sand, and clay. The younger (upper) Bidahochi contains ash and lava from volcanoes that erupted nearby and as far away as southwestern Nevada.