Death Valley Field Trip, page 3
Stop 5 Plant communities
Here by an alluvial fan we see pickleweed. There is an increase in salts as it approaches the valley. Plants have a different tolerance for salt and pickleweed is the most tolerant.
Stop 6 Tule Springs
Here grows mesquite, of which there are two species, honey and screwbean. Mesquite is concentrated along the spring line, the green stripe along the base of the alluvial apron. We can see Badwater Basin with its water from Amargosa River. There are lots of springs along this mesquite belt.
Stop 7 Panamint fault scarp
The Panamints have moved up while the valley floor has dropped down. The stretching has created normal faults. Since the Panamints are high the only evidence of faulting can be told by the erosion of the scarp. This pull apart basin started 14 million years ago, which is earlier than the Esmerelda Fm.
Stop 8 Eagle Borax Ruins
These old ruins has a mesquite thicket where spring water has come to the surface. There are also cattails and bulrushes which indicates there is always water present making this a salt marsh. This is the only place along the alluvial apron with water on the surface. The Hanapah fan, the largest along the Panamints, feeds this marsh. Borax was first found here. Borax is found in water and forms a white crust when the water evaporates.
Stop 9 Turtlebacks
Looking at the west side of the Black Mountains we see a turtleback, a geological formation. This name is only used in Death Valley. It is a arched surface of rock, an anticline, stripped clean of overlying debris. There is also a Copper Canyon turtleback. These are 100 million years old. They show that there can be compressional structures early and stretching later.
Stop 10 Shoreline Butte
Here at the south end of Death Valley is a little volcano formed as a result of the pull apart basin. This 690,000 year old volcano has been cut in half by a right lateral fault. To the south we can see Shoreline Butte where the horizontal lines are terraces created when a stable shore line cut into the basalt. The numerous terraces show the changing lake level. During the last ice age, about 700,000 years ago, Lake Manly was 300-400 feet deep here. The volcano was possibly formed in the lake or while there was a lower level. This butte is the only place where erosion has not worn away the lakeshore evidence. By contrast, Lake Walker (stop 1) was only 20,000 years ago. This was a pluvial lake. There were never any glaciers around Death Valley. The black outcrops we see toward the east are basalt flows that leaked up out of fault at the base of Black Mountains.