Arches National Park is 76,519 acres or 119 square miles long and lies in Utah. The park lies atop underground salt beds; basically a sea flowed into the region and eventually evaporated leaving behind the salt. The salt bed was eventually covered with an ocean that deposited sediments that accumulated and compressed to form sediemtnary rock. The salt beds were not stable under pressure and shifted and moved. Some sections of the rock were thrust upward into domes, while other sections dropped, and faults resulted, where arches could start to form. At one time the overlying layer of rock may have been more than a mile thick before erosional processes set to work. Fins are walls of more resistant rock that remain from differential erosion and arches form in fins. (http://www2.nature.nps.gov/geology/parks/arch/ ).
Landscape Arch, located in the park at Devils Garden, stretches over 300 feet in length and is one of the largest arches in North America. In 1973 it was decided that in order for a hole in the rock to be considered an arch it had to have an opening of at least three feet. Even if the opening is one inch high, as long as it is three feet long, it counts as an arch. (http://www2.nature.nps.gov/geology/parks/arch/).
In 1991 a slab of rock about 60 feet long, 11 feet wide and 4 feet thick fell from the underside of Landscape Arch, leaving behind an even thinner ribbon of rock. Luckily no one was injured and excitingly a person photographed it when it was in the middle of falling (http://www.arches.national-park.com/info.htm#geo).
Over 200 species of vertebrates and hundreds of species of invertebrates inhabit the park. Only with a keen eye will one see any organisms because they have adapted to the high desert conditions which means they’re not too active during the heat of the day. I remember starting the a hike on the Devil’s Garden Trailhead in the Park and seeing many lizards jetting into the shade, trying to avoid the sun as much as possible. Most animals simply avoid the extremes by staying in burrows or in the shade of a tree during the day and venturing out to feed in the evening. For example, the kangaroo rat, well known for its ability to tolerate desert environments, retreats underground during the day. (http://www.arches.national-park.com/info.htm#geo).
There are more than 100 other plant species in the park, but the rock formations impressed me more than any plant communities. Mountain mahogany and cliff rose often grow alongside and take advantage of the moisture that the Pinon and Juniper roots have penetrated (http://www.arches.national-park.com/info.htm#geo).
The beautiful scenery was something I had never seen before; looking out over miles and miles of land, arches, and canyons is certainly something I will never forget. I felt like Indiana Johns in the Last Crusade (http://www.moabutah.com/Resources/Arches.php). –Chris Matthews
I wanted to put the size of Arches National Park, which Chris mentions is around 77,000 acres, so, I looked up the approximate size of the White Mountain National Forest (WMNF) in New Hampshire and Maine and discovered that the WMNF is almost 10 times larger than Arches. While in Arches it is hard to get a sense of the scale because of the expansive vistas and in the White Mountain National Forest it is equally hard because it is so mountainous and one can only see a small segment at a time, unless one climbs to the top of Mount Washington.