The Sheep Mountain Range is one of 6 mountain ranges surrounding Las Vegas. It has heights up to 10,000 feet and valleys around 2,500 feet. Annual rainfall in the range varies from less than four inches in the valleys to over fifteen inches on the mountain peaks. The Range actively improves bighorn habitats by developing new water sources and maintaining and improving existing ones. Numerous other wildlife species share the range with bighorns. In addition to wildlife the Range also boasts an abundance of plant communities.
Plant communities and wildlife found on the Range vary with altitude and climate. Most of these plant species can be seen while driving the Morman Well Road (which can be accessed from the Corn Creek Field Station).The desert shrub community, composed of creosote bush and white bursage the dominant shrubs in the hottest, lowest elevations of Desert National Wildlife Range. Above the valley floor, Mojave yucca and cactus become abundant. At the upper edge of the desert shrub communities, between approximately 4,200 to 6,000 feet, black-brush and Joshua tree are dominant. Above 6,000 feet desert woodlands, composed of single leaf pinion, Utah juniper and big sagebrush begin. The coniferous forest communities begin around 7,000 feet. From 7,000 to 9,000 feet Ponderosa pine and white fir are the dominant trees. Near 10,000 feet where the growing seasons are the shortest, the only trees surviving are bristlecone pines.
The valley itself is a broad sedimentary basin at the southern end of the Basin and Range tectonic province, composed primarily of alluvial deposits weathered out of the mountains that surround the valley. The valley is geographically bounded by the Spring Mountains and Red Rock Canyon to the west, Frenchman Mountain and Lake Mead to the east, the McCullough Range to the south, and the Sheep and Las Vegas ranges to the north.
Now for the reason you came out here.
A natural arch:A rock formation with an opening underneath. Natural arches commonly form along cliffs where the cliffs are subject to erosion from the sea, rivers or weathering (subaerial processes); the processes “FIND” weaknesses in the rock & work at them, making them larger until they break through.
Pothole arches: Pothole arches form by chemical weathering as water collects in natural depressions & eventually cuts through the layers below.
Weather-eroded arches: Begin their formation as deep cracks which penetrate into lower layers. Erosion occurs within the cracks, wearing away exposed rock layers & enlarging the surface cracks. Alternating frosts & thaws causes crumbling & flaking of the porous rock and eventually cuts though. The resulting holes become enlarged by rockfalls & weathering. The natural processes that lead to selective removal of rock from a rock exposure are almost exclusively processes of erosion. Erosion can selectively remove rock both macroscopically and microscopically. Both modes are effective, albeit on different time scales, because of the basic structure of virtually all types of rock. Rock of any type (with the sole exception of a pure crystal) is a complex matrix of small, interlocking, solid particles. These particles are mostly microscopic fragments of various mineral crystals known as grains. Under high temperatures and pressures, some of the crystalline grains fuse, especially the smaller ones, and act as a cement between the larger grains.
Macroscopic erosion: occurs when joints or fractures are first induced in this rock matrix through some (usually catastrophic) process, and then widened through a variety of other processes. This splits the rock into distinct macroscopic pieces that can then move relative to each other under the forces of gravity or water pressure.
Microscopic erosion occurs when certain processes dissolve the crystalline cement, thus destroying the rock matrix and allowing other processes to disperse the remaining loose grains.
Both types of erosion occur separately and in combination on all rock exposures.
Only under very special circumstances will a natural arch form. These circumstances include the type, or types, of rock that are present, the shape of the rock exposure (especially in relation to the gravity gradient), and the combination of erosional processes that act upon it. Usually a very specific sequence of erosional processes must operate on a specific shape of rock exposure before a natural arch will form. Since some erosional processes are more effective on certain types of rock than others, the type of rock is also an important factor.
To get credit for this earth cache. Please answer the following questions by sending email with the below listed information.
Name of cache and GC code.
1. Which type of erosion was this and what is your reason for picking it?
2. The ledge located near ground zero is which of the rocks from the arch?Above the arch, the arch or below the arch
Bonus Point Take a picture of you and your group at the site with the arch in the background.