Western Kentucky University- Geol 476 Vegas

GEOL 475 - Western Kentucky University

Rainbow Basin:

Notes from Weldon Hawkins and Tyler Corn:

* in Baker, one can see the world’s tallest thermometer
* Also, don’t forget to stop in at the Mad Greek’s for gyros, milkshakes, and baklava

The midway point from a drive between Las Vegas and Los Angeles is a small town named Barstow. Just north of this town is a fantastic geologic site called Rainbow Basin. Managed by the Bureau of Land Management, this area contains an assortment of fossil bones, beautifully colored sedimentary rocks, and complex geologic structures. It is a great rest stop between Vegas and L.A., or it can be the subject of an all-day excursion. The first thing to notice once out of the car is the massive syncline, the axis of which trends directly through the basin. The thick red bed in the middle should help you spot it. A syncline is a geologic structure where the rocks have been folded in the shape of a smile. It is indicative of compressional geologic forces. To get a good look of this structure, try to find the axis of the syncline by looking at the east and west walls of the basin. Other than the massive red layer, do other strata catch your eye? White layers up to ten feet thick can be seen in the syncline. These layers are composed of volcanic ash and are called tuffs. Geologists love tuffs because they help document volcanic activity in the region and are useful for dating the adjacent strata. These tuffs are between 13 and 18 million years old and correlate with the fossil beds found in the basin. What else can you notice here? Facing the syncline (west wall, nearest the parking area), look to the left of the axis. A fault can be seen on the left (south) wing that transverses the entire basin. It is a part of the Calico fault system, which is similar to the more famous San Andreas fault. This fault occurred as continental plates slid past one another, displacing the rocks. In Rainbow Basin it caused a weakness in the strata, which accelerated erosional processes. Over time the basin eroded away to what we see today, leaving the fossils and structures in it exposed. The wings of the syncline form the walls of the basin. These steeply dipping strata are hard to scramble up, so if you want to walk around the rim of the basin, be careful. However, the views from this perspective may help you further grasp the beauty and complexity of Rainbow Basin.

Click on the thumbnails for more images of Rainbow Basin: