Physiographic features

This site occupies the lowest parts of the closed basin floor and is flat. It exists on the lower reaches of poorly defined drainage courses with no outlets and around the edges of shallow, land-locked lakebeds, Common landforms it is found on are: playa rims, playa lakes, relict lakebeds and depressions on alluvial valley floors. The playa dunes component is correlated to the sand hummocks ecological site.

Table 2. Representative physiographic features

Climatic features

The climate that typifies the High Intermountain Valley, ranges from arid to semi-arid, and is characterized by cold winters, moderate summers, and much sunshine. Average annual precipitation ranges from 6 to 10 inches along the valley floor and throughout most of the resource area. Upper elevations and southern reaches range from 11 to 13 inches. Precipitation extremes vary from 3 to 20 inches per year depending on location. The San Juan mountain range to the west and the Sangre de Cristo Mountains to the east intercept much of the precipitation causing a two-way rain shadow effect. Approximately 60 to 65 percent of the annual precipitation falls between May 1 and October 1, mostly from short duration high intensity thundershowers in July and August. Snowfall averages 34 inches annually; snow cover is light or patchy throughout much of the winter. Wind speeds average 7 miles per hour annually. High wind velocities are common in the spring.

Cold air from the encompassing mountain ranges drain into the valley and settle. This phenomena results in long cold winters and moderate summer temperatures. July is the hottest month and January is the coldest. Summer temperatures range from highs in the upper 70’s and low 80’s and occasionally reach to the mid 90o F. Summer nights are cool, with lows averaging in the mid 40’s. Temperatures of -20oF to -40oF can be expected each year and are common during some winters. Higher elevations can receive a dusting of snow as early as September 1. There is a 50% probability that the first frost in the fall will occur near September 16, and the last frost in the spring on about June 9. The average length of the growing season is 119 days and varies from 94 to 143 days. Summer humidity is low. Evaporation rates average lower than those of dry regions because of the cool climate.

Most major plant species initiate growth between mid May and late July, but growth may extend into September. Some cool season plants begin growth earlier and complete growth by mid June.

Table 3. Representative climatic features

Climate stations used

• (1) BLANCA 4 NW [USC00050776], Blanca, CO

• (2) ALAMOSA SAN LUIS AP [USW00023061], Alamosa, CO

• (3) MANASSA [USC00055322], La Jara, CO

• (4) MONTE VISTA 2W [USC00055706], Monte Vista, CO

• (5) CENTER 4 SSW [USC00051458], Center, CO

Influencing water features

A playa is an internally drained area that receives additional moisture from surrounding uplands by means of overland flow and throughflow. In the spring, due to snowmelt the playa system will experience ponding of surface water or at least a saturated soil profile to near the surface. On drier years, there may be no water table present within the profile. In a saline playa, the period transitioning from wet to dry status induces capillary water movement, facilitated by high clay content, from deep in the profile to the soil surface, where the moisture is transpired by plants or evaporated from bare soil. In either case, salts from within the profile are transported to the surface and accumulated through evapotranspiration.

The alkali overflow ecological site is associated with wetlands systems --hydric soils are common and wetland species, though intermittent with alternating wet and dry years, inhabit these sites—in that water tables are near the surface for some duration during the growing season. During wetter periods, the water table can be very near the surface, and water can even be ponded for long periods of time. As these playas dry out, they tend to form some type of salt crust, ranging from thin (1 mm or thinner) and discontinuous to thick (2 mm or thicker) and continuous for several square meters.

Soil features

The soils range from generally have clay loam surface texture with a subsurface (20 inches) of 30 to 40% clay., are derived from alluvium, are deep to very deep, and are underlain with sand or gravel. They are typically wet and are highly alkaline and saline. Water intake rates and subsoil permeability may be extremely slow, causing water to pond for significant periods following infrequent overflow periods. During dry periods, capillary action causes rapid loss of moisture from the surface and the formation of impermeable salt crusts.

Typical soil of this site is Biedell.

Table 4. Representative soil features

Animal community

Grazing:
This site has a medium value rating for cattle and sheep and a low value rating for horses.

Wildlife:
This site has a high value rating for cottontail and jackrabbit, a medium value rating for waterfowl, and a low value rating for antelope, bison, deer, elk, and upland game birds. Alkali overflow sites in the Blanca Wetlands area are of the few remaining breeding and nesting areas for Snowy Plovers in Colorado.

Hydrological functions

NA

Recreational uses

This site has a low value rating for recreation and natural beauty.

Wood products

NA

Other information

Rare, Threatened or Endangered Plants and Animals:
(To be added when known)

Inventory data references

Location of Typical Example of the Site:
Along lower drainage of San Luis Creek, 4 1/2 miles east and one mile south of Hooper on road to Medano Ranch.

Field Offices in Colorado Where the Site Occurs:
Alamosa, Center, and San Luis

References

• . 2021 (Date accessed). USDA PLANTS Database. http://plants.usda.gov.

Other references

Chapman, S.S., G.E. Griffith, J.M. Omernik, A.B. Price, J. Freeouf, and D.L. Schrupp. 2006. Ecoregions of Colorado. (2-sided color posterwith map, descriptive text, summary tables, and photographs). U.S. Geological Survey, Reston, VA. Scale 1:1,200,000.

Cleland, D.T.; Freeouf, J.A.; Keys, J.E.; Nowacki, G.J.; Carpenter, C.A.; and McNab, W.H. 2007. Ecological Subregions: Sections and Subsections for the conterminous United States. Gen. Tech. Report WO-76D [Map on CD-ROM] (A.M. Sloan, cartographer). Washington DC: U.S. Department of Agriculture, Forest Service, presentation scale 1:3,500,000; colored.

Soil Conservation Service (SCS). February 1977. Range Site Description for Alkali Overflow #314. : USDA, Denver Colorado.

United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296.

Contributors

C. Villa, H. Garcia, Scott Woodall
Suzanne Mayne-Kinney

Approval

Kirt Walstad, 9/07/2023

Acknowledgments

Project Staff:
Suzanne Mayne-Kinney, Ecological Site Specialist, NRCS MLRA, Grand Junction SSO
Alan Stuebe, MLRA Soil Survey Leader, NRCS MLRA Alamosa SSO

Program Support:
Rachel Murph, NRCS CO State Rangeland Management Specialist, Denver
Eva Muller, Regional Director, Rocky Mountain Regional Soil Survey Office, Bozeman, MT
B.J. Shoup, CO State Soil Scientist, Denver
Eugene Backhaus, CO State Resource Conservationist, Denver

--Site Development and Testing Plan--:
Future work to validate and further refine the information in this Provisional Ecological Site Description is necessary. This will include field activities to collect low-, medium-, and high-intensity sampling, soil correlations, and analysis of that data.

Additional information and data are required to refine the Plant Production and Annual Production tables for this ecological site. The extent of MLRA 51 must be further investigated.

Field testing of the information contained in this Provisional ESD is required. As this ESD is moved to the Approved ESD level, reviews from the technical team, quality control, quality assurance, and peers will be conducted.