Natural Resources Monitoring at Tonto National Monument
The Sonoran Desert Network monitors air quality, climate, groundwater, invasive exotic plants, landbirds, springs, seeps, and tinajas, and vegetation and soils at Tonto National Monument. The results of this work can be found in a variety of publications and other information. The network also maintains species lists for the park.
One of the first monuments to be designated under the Antiquities Act of 1906, President Theodore Roosevelt established Tonto National Monument to protect the stabilized (but unrestored) remains of two cliff dwelling complexes and numerous smaller prehistoric and protohistoric cultural sites. The location of these important prehistoric resources is directly related to the perennial waters, productive alluvial soils, and diverse natural resources of the Tonto Basin. People of the Salado culture inhabited the cliff dwellings for approximately 300 years, until around 1450 A.D.
Issues of concern relative to natural resources include preserving the park's small riparian area, unknown impacts of human presence on avian nesting activities, the introduction and spread of invasive exotic plants, and adjacent land-use activities, including grazing, increased recreational use, and alteration of the fire regime.
Setting and Key Resources
Size: 452 hectares
Elevation range: 431–1,219 meters
Tonto National Monument lies in the Tonto Basin, an inclusion of the Sonoran Desert nestled against the Mogollon Rim along the Salt River in central Arizona. The sharp escarpment of the Mogollon Rim separates the Sonoran Desert ecoregion from the Apache Highlands ecoregion. The proximity of the monument to this major transition is reflected in its diverse flora and fauna.
Considered some of the most rugged terrain in Arizona, slopes in the monument range from 2 to 90%. The monument rises high above a valley now filled by Roosevelt Lake, a 7,015-ha reservoir created by the completion of Roosevelt Dam in 1911. The monument lies on the southeastern flanks of the rugged Mazatzal Mountains, facing the even more precipitous Sierra Ancha Mountains to the northeast. These steep, angular mountains are typical of the Basin and Range physiographic province, with northwest–southeast aligned ranges separated by the Salt River Valley, which was the focus of prehistoric human uses in the region.
The northeastern third of the park is composed of alluvial outwash fans and bajadas emanating from the steep mountains that comprise the remainder of the monument. The monument contains three steep-gradient, ephemeral riparian systems: Cave Canyon, Deadman Canyon, and the smaller Cholla Canyon. The only perennial surface water in the park is Cave Canyon Spring.
The park occurs in three biomes: desert, thornscrub, and semi-desert grassland. Most of the elevational rise occurs within the space of three-quarters of a mile. Average annual precipitation is 16 inches (406 mm).
Local geology and soils
The Tonto Basin is an intermontane basin filled with a mixture of marine sediments and debris eroded from nearby mountains. The mountains in the region present today are the result of cycles of deposition, uplift, and erosion. Other landforms in the Tonto Basin include alluvial fans, bajadas, and pediments.
The geologic strata at Tonto National Monument are composed of the Precambrian Apache Group, and the entire Precambrian section is exposed in the monument. From oldest to youngest, the group includes Pioneer shale, Dripping Spring quartzite, Mescal limestone, and basalt. The Dripping Springs quartzite is notable because it houses the alcoves with cliff dwellings. The alcoves were created by weathering and erosional processes that likely started 50,000–400,000 years ago. The people of the Salado culture used sedimentary and igneous rocks in the area to form tools and building materials.
The park's soil families can be grouped based on where they occur on the landscape: hills, bajadas, or drainageways. The Bodecker and Tonto families occur in drainageways, with the Bodecker family in the Cave Creek riparian area and the Tonto family in areas of active wash cutting and sediment movement. The bajada or alluvial-fan soils include older surfaces that are mapped as Eba and Topawa families and the Tubac family, formed by erosion uncovering old, fine-grained lacustrine sediments. Hill or mountain soils include unstable steep colluvial sideslope soils mapped as Lampshire family, and several more stable summit soils that differ in composition based on age and composition of parent materials.
Biological soil crusts
Open spaces on the soils at Tonto National Monument are typically covered by biological soil crusts, a community of cyanobacteria, algae, lichens, and bryophytes. Lichens are a composite, symbiotic organism composed of a fungus and either a cyanobacteria or a green algae. Bryophytes are small, non-vascular plants, including mosses and liverworts.
Biological soil crusts provide key ecosystem functions. They increase resistance to erosion by water and wind, contribute organic matter, and fix atmospheric nitrogen. Cyanobacteria weave through the upper few millimeters of soil, binding soil particles together by secreting polysaccharides. The polysaccharides also contribute to soil aggregate structure, which is directly correlated with soil erosion resistance. Mosses and lichens have small, anchoring structures that help them protect the soil surface. On most soils, biological soil crusts increase infiltration.
The distribution and species composition of biological soil crusts is influenced by soil chemistry and disturbance. The recovery of biological soil crusts from disturbance depends on factors that include the climatic regime and type of disturbance. Generally, crusts recover slowly in areas with high annual temperature and low annual precipitation, such as Tonto National Monument. Biological soil crusts follow a recovery sequence in which, typically, cyanobacteria first colonize a site, followed by cyanolichens, other lichens, and then moss.
Climate and hydrology
Tonto National Monument experiences climate typical of the Sonoran Desert ecoregion: highly variable, bimodal precipitation with a considerable range in daily and seasonal air temperature, and relatively high potential evapotranspiration rates. From 1981 to 2010, 29% of the annual precipitation near the monument fell during thunderstorms from July through September, when maximum air temperatures can exceed 104°F and lead to violent (and often localized) rainstorms. The bulk of the remaining annual precipitation falls in relatively gentle events of broad extent from November through March. Average annual precipitation from 2006 to 2010 was 16.3".
Weather and climate data for Tonto National Monument and all other Sonoran Desert Network parks can be found at The Climate Analyzer, an interactive website that allows users to create custom graphs and tables from historical and current weather-station data. A weather and climate inventory was created for the Sonoran Desert Network in 2007. A more recent brief shows the magnitude and direction of ongoing changes in climate at Tonto National Monument.
Ephemeral stream channels run through the monument, with the exception of a small perennial section near Cave Canyon Spring, which emerges in Cave Creek below the Upper Ruin. Cave Canyon Spring may have been the water source for the Upper Cliff Dwellings. A spring at the confluence of Cave and Cholla canyons was likely the water source for the Lower Cliff Dwelling. However, this spring has not flowed since the early 1960s.
Human habitation of the Tonto Basin
Archaic people arrived in the Tonto Basin up to 10,000 years ago. Initially subsisting as hunters and gatherers, they eventually adopted agriculture and a more sedentary lifestyle. Irrigation of food crops along the upper Salt River and Tonto Creek by the Hohokam from the Salt and Gila river valleys began approximately 1,200 years ago.
From 1150 to around 1450, the Salado (Spanish for "salt," as named by archeologists working in the Salt River valley in the 1930s) lived in the Tonto Basin and occupied the monument's cliff dwellings. The Salado practiced subsidence agriculture along the river valleys and hunting and gathering on the higher elevations of the Tonto Basin. In the mid-1400s, the Salado migrated away from the Tonto Basin, an event that may have coincided with the arrival of the Apache. The Tonto Apache grew squash, corn, and beans, and there is evidence that they utilized fire to generate favorable conditions for hunting and gathering.
The local Apache and U.S. military began to clash in 1863, following the discovery of gold in the area. Subsequently, the U.S. military built several forts in the area, including Fort McDowell and Camp Reno. By 1875, the Tonto Apache were extirpated from the Tonto Basin, with many removed to the San Carlos Reservation. Decreasing violence in the Tonto Basin favored an influx of prospectors. The 1880 gold rush in nearby Payson drew additional Anglo settlement by merchants, farmers, and ranchers.
The construction of Roosevelt Dam from 1903 to 1911 brought more people to the area. Today, Globe and Payson are home to more than 7,500 and 15,000 people, respectively.
Invasive exotic plants
Biological invasions into new regions have increased at unprecedented rates in the past few hundred years. Once established, non-native plant species often lead to changes in ecosystem processes that in turn lead to functional and compositional change. In the American Southwest, historic and current land-management activities, such as livestock grazing and fire suppression, are thought to have helped make arid lands more vulnerable to invasion and subsequent loss of native species and biodiversity.
During a survey effort from 1999 to 2001, 28 non-native, introduced plant species were recorded at Tonto National Monument, 13 of which were grasses. Most of the other species were forbs, with one tree (tree tobacco; Nicotiana glauca) and one subshrub (horehound; Marrubium vulgare).
In 2005, another survey effort identified four problematic grass species that were widespread: wild oat (Avena fatua), red brome (Bromus rubens), ripgut brome (Bromus rigidus), and Lehmann lovegrass (Eragrostis lehmanniana). Buffelgrass (Pennisetum ciliare) and Sahara mustard (Brassica tournefortii) were also noted as problematic.
Natural/cultural resource conflicts
Tonto National Monument contains substantial and spectacular natural and cultural resources whose respective management practices sometimes come into conflict. For example, unmanaged vegetation growth can damage architecture, displace artifacts, and create fire hazards. It is often necessary to remove and thin vegetation in and around architectural elements in order to protect the structural integrity and information potential of archeological sites. However, removing vegetation can exacerbate erosion problems by decreasing the amount of total cover. Sonoran Desert Network staff have provided park managers with several options for managing the natural resources at sites that may protect cultural resource values.
Sensitive aquatic and riparian resources
The small riparian area along Cave Creek, associated with Cave Canyon Spring, has been identified as the most important biological resource in the monument. While riparian areas account for only 1% of the land cover in the Southwest, most animals depend on riparian areas for all or part of their life cycles. Riparian vegetation also provides many other benefits, or ecosystem services. They slow flood flows, stabilize stream banks, enhance aquifer recharge, filter water, and provide wildlife habitat.
The riparian area at Tonto National Monument provides habitat for six species of frogs and toads. In addition, the yellow-billed cuckoo (Coccyzus americanus) has been identified in the riparian area. The yellow-billed cuckoo is listed as a threatened species by the State of Arizona, and a candidate species by the U.S. Fish and Wildlife Service. A biological inventory for the park provides more detail. The majority of the Cave Canyon watershed occurs upstream of the monument, on the Tonto National Forest. Therefore, activities occurring upstream on the forest impact Cave Canyon and its spring.
When the National Park Service assumed responsibility for Tonto National Monument in 1934, 7,000 people visited the monument. Annual visitation exceeded 50,000 in 1961 and peaked at over 82,000 in 1986. Since 2001, the monument has averaged over 60,000 visitors per year. Visitation tends to peak from January through April.
Adjacent land use
The U.S. Forest Service manages the 2.8-million acre Tonto National Forest, which surrounds Tonto National Monument and stretches from Phoenix north to the Mogollon Rim. Portions of the monument were grazed until 1974. Construction of a boundary fence took place from 1979 to 1981, when non-native ungulates were excluded from the monument. Today, grazing continues on the adjacent Tonto National Forest.
Last updated: November 30, 2018