I-17 Roadside Geology & Old Indian Salt Mine
We traveled to a site near Camp Verde, AZ to get our first taste of Arizona/Mars Analog geology. For many of us, it was a literal taste. The primary feature of the site were the clay soils, mudstone, displacement growth crystals (desert roses or gypsum) and halites. The latter being the mineral of taste and the namesake of the site.
Following I-17 out of Tempe to Camp Verde, the road cuts revealed many of the rock layers and geologic history of the Basin & Range and transition to the Central Highlands.
We hiked into the site from the road side. The texture of the soil was soft and slippery, being primarily clay. Without a distinct crystal structure, the particles don't bind under foot as sand or other soils. Just under the grey-brown surface was a chalky white powder, the consistency and feel of cornstarch. This fine white dust coated everything.
The desert roses were nearly everywhere. Some sitting on the surface or poking up from just below. Others only a few centimeters below the surface and easily found by digging with a spoon. I collected several to photograph including one specimen that is a nearly perfect gypsum rhombohedral crystal about 2.5 cm on edge and about 0.5 cm thick.
At the bottom of a slope, there was a ravine littered with a wide variety of cobbles ranging from 20 cm to 40 cm. In one spot I found a grouping of 5 distinctly different rocks in one square meter. Among theses was an unusual grey granitic rock. I appeared to be basalt, fine grained, but less dense than one would expect. It also had several small pockets 2 mm to about a centimeter in diameter. The larger ones seemed to be gypsum, the smallest were a brown-green crystals slightly larger than the surrounding grain. I broke up a piece to bring back some specimens for further observation.
David Blake NASA Ames CheMin PI gave a demo of how MSL Curiosity analyzes the chemical-mineral content of rock samples on Mars. Using the percussive drill at the end of the robotic arm, about 10 cubic mm of rock dust
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