Mountain soils range from gently sloping to very steep. These soils are deep, highly porous, sandy and are underlain by gravelly subsoils. In some cases there are rocky outcrops. The prevailing soils in the San Juan Mountains are derived mainly from weathering and erosion of volcanic rocks. Among others, these include the Seitz, Frisco, Granile, and Bendire complexes. These soils are used principally for livestock grazing and timber production. The most common native vegetation consists of western wheatgrass, blue grama, piñon and ponderosa pine, juniper, oak, and blue spruce with an understory of sideoats grama, and mountain muhly. While the foot slopes can be cultivated with irrigation, they are leachy and do not retain moisture.
In the Sangre de Cristo Mountains, the parent material is primarily outwash derived from granite, gneiss, mica schist, and sedimentary rock. Common soils include the Teewinot, Leadville, Stunner, Uracca, and Lakehelen complexes, which range from deep and well drained stony and sandy loams to bedrock outcrops in the higher elevations. Common uses include livestock grazing, timber production, and natural pastureland.
Valley soils are primarily classified as San Luis, Gunbarrel, Mosca, Hooper, Alamosa, and Travelers soil complexes. These are deep alluviums typically composed of sandy loams, loams, or clay loams underlain by gravelly subsoils that formed from igneous and metamorphic rock. Compared to the mountain soils, these are darker in color, and have a heavier texture and more compact structure.Generally speaking, these soils are poorly drained, typically alkaline, very low in organic matter, and subject to waterlogging. In some cases, depth to water table ranges from 12 to 40 inches. These soils occur along the tributary stream bottoms and alluvial fans, and over extensive areas of the valley floor. They represent the most common soil types of the southern and western parts of the larger San Luis Valley.
These soils are well adapted to grains, alfalfa, grasses, field peas, and vegetables, including the root crops. Principal native plants associated with these soil types include saltgrass, alkali sacaton, rabbitbrush, and greasewood, as well as sedges and rushes in the wetland and riparian areas.
Ecoregions Containing alluvial valleys, volcanic plateaus, alpine and subalpine forested mountains, shrubland-covered hills, sand dunes, sand sheets, salt flats, wetlands, and a variety of aquatic habitats, the ecological diversity of the Sangre de Cristo National Heritage Area is enormous. Its landscape comprises 12 of Colorado’s 35 Level IV Ecological Regions, the most detailed categorization of ecological regions defined by the US Environmental Protection Agency. Each ecoregion represents an area that is similar in geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology; they are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems and ecosystem components, especially across federal agencies, state agencies, and nongovernmental organizations that are responsible for different types of resources within the same geographical areas.
Ecoregions within the Sangre de Cristo and San Luis mountain zones are principally determined by geology and elevation. They include the Alpine Zone, Crystalline Mid-Elevation and Subalpine Forests, Sedimentary MidElevation and Subalpine Forests, Volcanic Mid-Elevation and Subalpine Forests, and Foothill Shrublands.
The Alpine Zone makes up a small percentage of the heritage area. Found along the highest peaks of the Sangre de Cristo and San Luis mountain ranges, these are treeless glaciated areas with steep slopes and exposed rocky peaks that rise above the timberline at an elevation of 10500 to 11,000 feet. The amount of precipitation received within this zone is the highest within the heritage area – between 35 and 70 inches per year – and its snowmelt serves as a water source to the lower elevations. Its principal land cover includes snowpack, ice, bare rock, and alpine meadows containing bistort, alpine timothy, alpine avens, alpine bluegrass, alpine clover, tufted hairgrass, and various sedges. The forest-tundra interface is sparsely colonized by stunted Englemann spruce, subalpine fir, and limber pine (krummholz vegetation). Some of the oldest recorded trees in North America, the Rocky Mountain bristlecone pine, can also found here, some of the oldest recorded trees in North America.
The Crystalline and Sedimentary Subalpine Forests occupy most of the Sangre de Cristo Mountain Range within the heritage area, whereas the Volcanic Subalpine Forest occupies most of the San Luis Mountains. Distinguished by their bedrock, these are high mountain and steeply sloped, glaciated zones that range between 9,000 and 12,000 feet in elevation. Found below the Alpine Zone, they receive slightly less precipitation – between 28 and 50 inches per year (the Crystalline Subalpine Forest receiving slightly more), which persists as deep winter snowpack. Forests within these zones are dominated by Engelmann spruce and subalpine fir that are often interspersed with aspen groves, lodgepole pine, or mountain meadows, and with Douglas fir at lower elevations. The Crystalline Subalpine Forest understory is dominated by dwarf huckleberry and grouse whortleberry, whereas the Sedimentary and Volcanic Subalpine Forests contain more kinnickinnick, snowberry, sedges, mountain brome, and forbs. Perennial streams are also found in this zone.
The Crystalline, Sedimentary, and Volcanic Mid-Elevation Forests are partially glaciated. The Crystalline and Sedimentary Mid-Elevation Forests occupy only a small portion of the heritage area east of Garland City in Costilla County, whereas the Volcanic Mid-Elevation Forest comprises a small zone west of Fox Creek and Centro in Conejos County. These ecoregions occupy an elevation ranging between 7,000 and 9,000 feet. Their forests are characterized by low mountain ridges, slopes, and outwash fans that receive between 20 and 32 inches of precipitation per year. The Crystalline Mid-Elevation Forest vegetation consists primarily of Ponderosa pine with areas of Douglas fir, and an understory of mountain mahogany, bitterbrush, wax currant, skunkbush, woods rose, mountain muhly, Junegrass, Arizona fescue, king spike-fescue, and various sedges.
The Sedimentary Mid-Elevation Forests contain more Gambel oak woodland, aspen forest, and two-needle piñon pine, as well as antelope bitterbrush, fringed sage, serviceberry, and snowberry. Volcanic Mid-Elevation Forests differ in that their understories contain more dwarf juniper, western wheatgrass, Oregon grape, blue grama, sideoats grama, and needlegrasses.
The Foothill Shrublands comprise a narrow zone at the foothills of both the San Luis and Sangre de Cristo mountain ranges. Mostly occupying an elevation range of 6,000 to 8,500 feet, they can extend up to 10,000 feet in small areas. This ecoregion is unglaciated and contains perennial as well as intermittent and ephemeral streams. Receiving a mean annual precipitation of 12 to 20 inches, it consists of mostly sagebrush, as well as some areas of piñonjuniper woodland that are interspersed with mountain mahogany shrubland, Gambel oak, mountain big sagebrush, skunkbush, serviceberry, fringed sage, and rabbitbrush, as well as such grasses as blue grama, Junegrass, western wheatgrass, Indian ricegrass, Scribner needlegrass, and muttongrass. Ecoregions within the valley area include Salt Flats, Sand Dunes and Sand Sheets, San Luis Alluvial Flats and Wetlands, and San Luis Shrublands and Hills.
The San Luis Shrublands and Hills are found throughout much of the southern portion of the heritage area and encompass the San Luis Hills, Taos Plateau, and the lower foothills of both mountain ranges. Ranging between 7,900 to 9,100 feet in elevation, this ecoregion’s mean annual precipitation averages between 10 and 14 inches per year. The lands are primarily used for rangeland and contain shrublands, grasslands, and piñon-juniper woodlands at their highest elevations. Species include big sagebrush, rubber rabbitbrush, winterfat, western wheatgrass, green needlegrass, blue grama, and needle-and-thread grass.
The San Luis Alluvial Flats and Wetlands ecoregion covers extensive areas of the San Luis Valley. In Alamosa County it extends along most of its western border and as far south as Antonito in Conejos County. Another large area is found in a stretch along Route 159A extending south from Blanca to the state line, and another extending southwest from San Luis to the Rio Grande. As its name suggests, it is a relatively flat area containing wetlands, springs, and areas with a high water table. It also hosts several large perennial streams that originate in the mountains. Ranging from 7,500 to 8,000 feet in elevation, it receives only 6 to 10 inches of precipitation per year. This ecoregion generally corresponds with irrigated cropland, which has replaced most of the natural vegetation (shadscale, fourwing saltbush, and greasewood). The most common crops include potatoes, alfalfa, barley, hay, and wheat, as well as small areas of vegetables such as lettuce, spinach, and carrots.
The Salt Flats comprise some of the lowest lying areas of the heritage area. They extend from the north boundary of the heritage area southward to the vicinity of La Sauses, making up approximately half of Alamosa County. This ecoregion receives only 6 to 8 inches of precipitation per year. Unlike the Alluvial Flats and Wetland ecoregion, however, most of these lands are not irrigated and remain in shrubland that are adapted to the alkaline soils (shadscale, fourwing saltbush, greasewood, horsebrush, spiny hopsage, rubber rabbitbrush, saltgrass, and alkali sacaton). Much of this region is used as low-density pastureland.
The Sand Dunes and Sand Sheets are located in and around the Great Sand Dunes National Park. This ecoregion is characterized by the dunes themselves, as well as the sandy grasslands that extend around three sides of the main dunefield, also known as the sand sheet. Almost 90 percent of the sand deposit is found in the sand sheet, while only about 10 percent is found in the main dunefield. The sand sheet is the primary source of sand for the Great Sand Dunes. Small dunes form here and then migrate into the main dunefield (NPS, Great Sand Dunes). Comprising a unique ecosystem, this area has outstanding biodiversity significance. While the dune areas are mostly devoid of vegetation, some Indian ricegrass, blowout grass, and lemon scurfpea can be found here. The sand sheet plant communities are characterized by rabbitbrush, needle-andthread grass, and rice grass, while scurf pea, skeleton weed, and blowout grass characterize the shifting sand component. Some of the sand sheet is used as native pastureland for bison and cattle.