The Sonoran Desert National Monument contains more than 496,000 acres of diverse Sonoran Desert landscape. The Sonoran Desert is the most biologically diverse of the North American deserts and the monument captures a significant portion of that diversity. The most striking aspect of the plant community within the monument is the extensive saguaro cactus forest. The monument contains three distinct mountain ranges, the Maricopa, Sand Tank and Table Top Mountains, as well as the Booth and White Hills, all separated by wide valleys. The monument also contains three Congressionally designated wilderness areas and many significant archaeological and historic sites and remnants of several important historic trails.
Introduction
The Sonoran Desert National Monument is a magnificent example of untrammeled Sonoran desert landscape. The area encompasses a functioning desert ecosystem with an extraordinary array of biological, scientific and historic resources. The most biologically diverse of the North American deserts, the monument consists of distinct mountain ranges separated by wide valleys and includes large saguaro cactus forest communities that provide excellent habitat for a wide range of wildlife species. The Sonoran Desert National Monument is in south central Arizona. The outer boundaries of the area encompass approximately 500,000 acres of land, approximately 408,646 acres of which are owned by the federal government and managed by the Bureau of Land Management (BLM) and approximately 77,957 acres of which are under the joint jurisdiction of the BLM and the Department of Defense.
History & Culture
The Sonoran Desert National Monument contains many significant archaeological and historic sites, including rock art sites, lithic quarries and scattered artifacts. Vekol Wash is believed to have been an important prehistoric travel and trade corridor between the Hohokam and tribes located in what is now Mexico. Signs of large villages and permanent habitat sites occur throughout the area and particularly along the bajadas of the Table Top Mountains. Occupants of these villages were the ancestors of todays O’odham, Quechan, Cocopah, Maricopa and other tribes. The monument also contains a much used trail corridor twenty miles long in which are found remnants of several important historic trails, including the Juan Bautista de Anza National Historic Trail, the Mormon Battalion Trail and the Butterfield Overland Stage Route.
Nature & Science
Geology
Sonoran Desert National Monument is located within the Desert Region of the Basin and Range geologic province of southwestern Arizona. This region is characterized by steep, rocky, alternating mountain ranges separated by broad, gently sloping to nearly flat, deep, broad valleys formed by faulting that occurred approximately 5 to 15 million years ago. Most of the mountain ranges have been formed by faulting, flooding, or volcanism. The broad valleys are generally underlain by thick deposits of gravel, sand and silt. The monument also contains numerous areas of rocky “desert pavement,” where fine alluvial material has been removed. Desert pavements are slow to form and extremely fragile. A thin, hardened surface layer called “desert varnish” may occur on desert pavement. Desert varnish acts as a cement, holding surface soils together and protecting them from wind and water erosion. When the crusty layer of desert varnish is disturbed, underlying soils are subject to erosion and compaction. The time required to form desert soils can range from hundreds to thousands of years. Without such soil, most plant life cannot survive.
The “basin and range” country includes numerous high peaks and low valleys. The 4,373 foot, basalt-capped Table Top Mountain dominates the topography on the east end of the monument. Its flat-topped summit is easily seen and recognized as far away as the outskirts of Phoenix, 45 miles to the north and Casa Grande, 20 miles to the east.
The Maricopa Mountains are lower, with one peak as high as 3,300 feet, but dozens between 2,000 and 3,000 feet in elevation. The alluvial valleys near the Maricopas descend to as low as 800 feet above sea level. The relief is similar in the Sand Tanks, where the highest point reaches over 4,000 feet. The wide, flat wash that cuts through the heart of the Vekol Valley descends only about 300 feet in elevation over 12 miles, from the monument’s southern boundary to Interstate 8.
Ecology
The Sonoran Desert National Monument’s biological resources include a spectacular diversity of plant and animal species. Some of the higher peaks include unique woodland assemblages, while much of the lower elevation lands offer one of the most structurally complex examples of palo verde/mixed cacti association in the Sonoran Desert. The dense stands of leguminous trees and cacti are dominated by saguaros, palo-verde trees, ironwood, prickly pear and cholla. Important natural water holes, known as tinajas, occur in the monument.
The most striking aspect of the plant communities within the monument are the saguaro cactus forests. The saguaro is a signature plant of the Sonoran Desert. Individual saguaro plants are indeed magnificent, but a forest of these plants, together with the wide variety of trees, shrubs and herbaceous plants that make up the forest community, is an impressive site to behold. The saguaro cactus forests within the monument are a national treasure, rivaling those within the Saguaro National Park.
The rich diversity, density and distribution of plants in the Sand Tank Mountains area of the monument is especially striking and can be attributed to the management regime in place since the area was withdrawn for military purposes in 1941. In particular, while some public access to the area is allowed, no livestock grazing has occurred for nearly fifty years. To extend the extraordinary diversity and overall ecological health of the Sand Tanks Mountains area, land adjacent and with biological resources similar to the area withdrawn for military purposes should be subject to a similar management regime to the fullest extent possible.
Scientific analysis of a pack rat midden from Area A shows that the area received far more precipitation 20,000 years ago and slowly became more arid. Vegetation for the area changed from juniper-oak-pinion pine woodland to the vegetation found today in the Sonoran Desert, although a few plants from the more mesic period, including the Kofa Mountain barberry, Arizona rosewood and junipers, remain on higher elevations and north-facing slopes.
The lower, flatter areas of the monument contain the creosote-bursage plant community. This plant community occurs over the open expanses between the mountain ranges and connects the other plant communities together. Rare patches of desert grassland also occur in the Sand Tank Mountains area. The washes in the area support a much denser vegetation community than the surrounding desert, including mesquite, ironwood, paloverde, desert honeysuckle, chuperosa and desert willow, as well as a variety of herbaceous plants. This vegetation offers the dense cover bird species need for successful nesting, foraging and escape and birds heavily use this plant community during migration.
The diverse plant communities present in the monument support a wide variety of wildlife, a robust population of desert bighorn sheep, especially in the Maricopa Mountains area and other mammalian species such as mule deer, javelina, mountain lion, gray fox and bobcat. Bat species within the monument include the endangered lesser long nosed bat, the California leaf-nosed bat and the cave myotis. Over 200 species of birds are found in the monument. Numerous species of raptors and owls inhabit the monument including the elf owl and the western screech owl. The monument also supports a diverse array of reptiles and amphibians, including the Sonoran desert tortoise and the red-backed whiptail. The desert tortoise occupies approximately 25,000 acres of habitat in the Maricopa Mountains.
Recreation
The Sonoran Desert National Monument provides numerous opportunities to learn about prehistoric and historic sites. Additional activities include wildlife viewing, camping, hiking, hunting and back-country vehicle travel. Off highway vehicle use is prohibited. No motorized and mechanized use of vehicles and equipment is allowed in wilderness.
Traveler Facts
Contact Information
Sonoran Desert National Monument
BLM Phoenix Field Office
21605 North 7th Avenue
Phoenix, AZ 85027
Phone: 623-580-5500
Location
The Sonoran Desert National Monument is in south central Arizona, 60 miles from Phoenix. Interstate 8 provides some access at the Vekol interchange (Exit 144) and the Freeman Interchange (Exit 140). State Highway 238 (Maricopa Road) affords access to the North Maricopa Mountains and the Butterfield Overland Stage Route.
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