Just outside of the town of Escalante in Utah is the Escalante State Park, also known as the Escalante Petrified Forest State Park. The park sits on the shores of the Wide Hollow Reservoir, which is a great little reservoir to swim in or boat and fish. But the geological destination for this park is the Nature Trail, also known as the Petrified Forest Trail. Along the trail, large petrified trees are easily visible. Although not as densely packed with trees as Petrified Forest National Park, this is still a fantastic view of the logs in an unexpected location.
Monday, November 15, 2021
Geological Destination - Escalante Petrified Forest State Park
Many of the logs are easily visible from the trail. The park itself preserves about 5.5 million tons of petrified wood across the 1,400 acres. These logs had been petrified, which is a type of fossilization specifically referring to trees. The wood molecules had been slowly replaced over time by molecules of minerals, in this case silica, also known as quartz. Over time all of the wood molecules would have been replaced with the silica creating a tree shaped rock that preserves many of the intricate details from the tree itself. These details include the tree rings and bark.
The state park sits right in the middle of several National Parks including Grand Staircase-Escalante National Monument to the south and Capitol Reef National Park to the north.
The logs sit within the Brushy Basin Member of the Morrison Formation from the Late Jurassic (~130-140 million years old). The wood is thought to have eroded out of the overlying conglomeratic part of the Brushy Basin and tumbled down the slope to the lower mudstone, where it sits now. The mudstone then erodes much more easily than the harder, and heavier, quartz logs, so the logs remain behind as the other material is washed away/eroded over time.
The petrified wood layer within the Brushy Basin Member is one of the youngest layers of the Morrison Formation. This stratigraphic section is from the Utah Geological Association Publication of the Escalante State Park Geologic Trail Guide.
During the hike you get a pretty good overview of the campground and the reservoir as well as the various layers of the Brushy Basin from the caprock of the area, the conglomeratic unit, to the underlying softer mudstone.
The trees were deposited within a braided stream system, much like the above braided stream system from Banff National Park in Canada. These streams are often slow moving stream systems with periodic large amounts of water, so they are able to move a large array of sediment sizes from sand to gravels, and even large pebbles and boulders. These sediments are often more varied and larger than are frequently found in more meandering streams like the Mississippi River. The trees in this park would have likely grown up on the banks of the river, when they were uprooted and rolled along the river until they came to rest in the gravel and sand channel.
View of one of the logs highlighting the rings. The trees in the park are not of the best preservation to be able to identify them very well. However, some of the trees had been identified as conifers, however the level of preservation is not fine enough to be able to identify which species of conifer.