1857 Stone Polygons in Southern Colorado, USA: Observations of Suricial Activity 1975–2004 John D. Vitek Ofice of Graduate Studies & High Altitude Research Program (HARP), Texas A&M University, College Station, TX, USA Netra Raj Regmi HARP & Geology & Geophysics Department, Texas A&M University, College Station, TX, USA Daniel Humbolt Electrical & Computer Engineering, Texas A&M University, College Station, TX, USA John R. Giardino HARP, Geology & Geophysics Department, Geography Department, & Water Management & Hydrological Sciences Program, Texas A&M University, College Station, TX, USA Abstract Small stone polygons occupy a depression at 3865 m in the Sangre de Cristo Mountains, southern Colorado, USA. Vertical photographs were collected between 1975 and 2004 to document natural change on the surface of these polygons. Over time, the stones in the core region of these small polygons moved in multiple directions rather than directly toward the edges of the polygons. Clearly, movement results from freeze-thaw forces in three-dimensions within the polygons and from forces generated by water freezing in the stone gutters. Smaller polygons formed within the larger unit. Some stones observed in 1975 disappeared by 2004, essentially moved into the edges of the polygon and rotated such that identiication becomes dificult. Measured horizontal displacements reached 29 cm, although the average is 7.4 cm for all stones. Maps of change and vectors of motions reveal the dynamic aspects of three dimensional forms subjected to intense freeze-thaw in an alpine environment. Keywords: displacement; frost processes; repeat photography; stone polygons. Introduction Stone polygons, forms of patterned ground that are common in arctic and alpine areas, are generally attributed to intense freeze-thaw processes (Washburn 1956). In the years since Washburn’s comprehensive review, numerous researchers have reported on many aspects of patterned ground in various locations (Washburn 1979, French 1996, Hallet et al. 2004) and attributed them to numerous processes of formation. Additional research will be cited with speciic information as this paper is developed rather than simply listing them in this introduction. Vitek (1983) reported on seven years of suricial activity observed on stone polygons found in a small depression in glacial till at 3865 m in the Blanca Massif of the Sangre de Cristo Mountains in south-central Colorado. This paper extends the record of those initial observations to 30 years. In total, observations were made 22 times from 1975–2004. On several occasions, observations could not be obtained because the stone polygons in the 850 m 2 depression in a cirque were underwater from snowmelt and precipitation. Since the site was irst observed in 1975 until the last visit in 2004, standing water during the growing season is a major deterrent to grasses occupying the depression. Occasionally small tufts of grass appear but seldom do they survive the harsh winters. The lack of vegetation suggests that frost processes are not impeded and readily move stones around the surfaces of the polygons. The site is very remote, a ive hour hike from the nearest road, and is not on any marked trail, nor would a causal hiker venture into this area because of the lack of access to high peaks, i.e. those above 4300 m .a.s.l. Aside from an occasional small animal print embedded in the center of a polygon, the site has been virtually undisturbed. Every effort was made during photography to retain the site as undisturbed. This paper presents observations, analyses of these observations, and discusses the forces involved in creating these stone polygons and movements of stones in the center of several polygons. How these observations relate to published research will be described in the discussion section along with suggestions for future research at this site. Whereas these observations represent changes in a suricial plane, stone polygons are three-dimensional phenomena. Within the centers of these small polygons, smaller polygons have been observed; they form either from desiccation drying or are the remnants of frost polygons left over from winter. Movement vectors reveal that motion is possible in many directions rather than just toward the edges of the polygons. We present only total change from 1975– 2004 in this paper rather than the incremental changes that are possible with the data that have been collected. Greater detail will be published in a subsequent paper. Study Area The Sangre de Cristo Mountains are located in south- central Colorado (Fig. 1). Extensively glaciated during the Pleistocene, the Blanca Massif portion of the range contains numerous sites with patterned ground. Large stone polygons (Vitek & Tarquin 1984, Berta 1988, Vopata et al. 2006) are