7 October 2017, Saturday
Goose Island Camp, La Sal Mountain Loop
We have been viewing the La Sal Mountains from a distance all week. Today, following a route in O’s geology book, we drive into these mountains as we read about geologic features we can view from the road. We begin in a clockwise direction along route 128, the road our campground is on, to the La Sal Mountain loop road. There is a sign at the turn off saying the road is closed for construction in 16 miles. We will drive as far as we can, and then turn around and drive up the loop road in the opposite direction, from its southern end south of Moab.
The La Sal Mountains are laccoliths, 30 million year old igneous intrusions into sedimentary rock. The sedimentary layers are softer than the igneous rock and wear away over time. The igneous rock of the La Sal Mountains erodes much more slowly. Meanwhile, a giant salt dome beneath the adjacent sedimentary layers is dissolving away. The salt is present in this area because there was once a giant inland sea here. As layers of sediment accumulated over salt layers left by evaporation about 290 million years ago, the pressure caused the salt to be squeezed upward into a dome. The overlying sedimentary layers were fractured. Surface water could now seep down and dissolve away the salt. Eventually the dome collapsed leaving behind the Spanish/Moab Valley, surrounded by the cliffs left behind as the central area fell. Apparently this process is ongoing.
O and I drive from the valley, up through sedimentary layers. From the north end of the loop we see some interesting monuments standing on a cliff top. The formation is called (from left to right) the priest, the nuns and the rectory, and at the end stands imposing Castleton Tower.
About 12.5 miles into our loop we reach a “road closed” sign. We turn around and drive south through Moab to the other end of the loop. From here, the road climbs quickly from the valley floor which is at about 4000 feet, to almost 8000 feet. As we climb there is a marked change in vegetation, from scrubby desert brush to pine and aspen forests. The trees are a welcome sight to O and me after 2 weeks of desert landscape. The aspens are turning a beautiful golden color in the cool autumn days. The tapestry of color clothing the mountainsides is breathtaking. As we round one of the switchbacks a golden eagle soars above. We wind up the mountain road as far as we can, and then turn around and enjoy the spectacular views once again as we drive back down.
At the Spanish Valley Overlook we can see one of the faults from the salt dome collapse. We return to camp for dinner as shadows lengthen.
