Sliding stones, Racetrack Playa, California ROBERT P. SHARP Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 DWIGHT L. CAREY Department of Geology, University of California at Los Angeles, Los Angeles, California 90024 ABSTRACT 1952a, 1952b; R. E. Kirk, 1953; Shelton, any other playa. Some immutable law of 1953; Stanley, 1955; Schumm, 1956; Clem- nature probably prescribes that movements Twenty-eight of 30 monitored stones on ents, 1958; W. E. Sharp, 1960; Creutz, occur in the darkness of stormy moonless the southern part of Racetrack Playa moved 1962; Bradley, 1963; Findley, 1970). This nights, so that even a resident observer within a seven-yr interval, leaving distinct playa is not unique, as stone tracks have would see newly made tracks only in the tracks. Movements occurred principally been reliably reported on at least eight dawn of a new day. Tracks made by objects during the winters of 1968-1969, 1972- other dry lakes in southeastern California moved by other mechanisms in different 1973, and 1973-1974. Some stones moved and adjacent Nevada (Table 1). However, geological settings contribute little to the in all three episodes, some only in one or Racetrack Playa is distinguished by the playa-track problem (Sainsbury, 1956; Di two, and a few on other occasions. Move- great number and large size of stones and Cesare and Pratelli, 1967; Hattersley- ment is clearly related to wet stormy an abundance of tracks. Smith, 1969, p. 45; Dionne, 1969). The weather. We realized in April of 1968 that no sys- moving stones and their tracks are hardly Greatest cumulative movement, 262 m, tematic observation of stone movements matters of greatest scientific import, but and greatest single-episode movement, 201 was being maintained, and so permission broad interest in this curious phenomenon m, were by a small, 250-g stone. Other was obtained from then incumbent Monu- motivated the investigation. monitored stones weighing as much as 25 ment Superintendent, John W. Stratton, to kg moved cumulative distances of 60 to 219 establish a monitoring program. The objec- PHYSICAL SETTING m. Net direction of movement was north- tives were to determine the season, fre- AND CONDITIONS northeasterly with deviations to east and quency, conditions, direction, and mag- southeast on occasions by some stones. nitude of stone movements, their relation- General Movement most likely occurs within one to ships to meteorological conditions, the pos- several days after playa wetting, and ve- sible role of ice, and to confirm or challenge The playa lies at the southern end of locities on the order of 0.5 to 1 m/sec are in- the generally prevailing opinion that wind topographically closed Racetrack Valley, ferred from track characteristics. is the motivating force. Observations from nestling between two northward-projecting Thin sheets of ice form in winter on this May 1968 to May 1975 were made mostly prongs of the Panamint Range (Fig. 1). The playa, and eyewitness accounts of ice during weekend visits on 16 occasions. elliptically shaped lake floor, 1,130-m ele- sheets, some with infrozen stones, being No authenticated record has been dicov- vation, is 4.5 km north-south and 2.1 km driven by wind across other southern ered of anyone seeing a stone actually make wide. Closely bordering bedrock ridges rise California playas indicate that stone tracks a track by natural means on Racetrack or above 1,830-m elevation, and Ubehebe may be made in this manner, as earlier ad- vocated. However, movement of stones out TABLE 1. PLAYAS IN SOUTHEASTERN CALIFORNIA AND of an encirclement of iron stakes, large ADJACENT NEVADA DISPLAYING STONE TRACKS changes in neighboring stone separation during movement, disproportionate corre- Playa Location Source of information (lat long) sponding reaches within contemporaneous tracks of neighboring stones, and other re- Racetrack Calif. (36°41'N, 117°34'W) McAllister and Agnew lationships strongly suggest that monitored (1943) stone movements occurred without the aid Little Bonnie Claire Nevada (37°10'N, 117°10'W) Clements of extensive ice sheets. (1952) Wind acting directly on the individual Nevada (35°51'N, 114°57'W) Stanley stones is considered the prime moving Nelson Dry Lake (1955) force. A critical element promoting move- ment may be deposition of a thin layer of Rogers Calif. (34°55'N, 117°47'W) Motts fine slippery clay, the material that last set- (1969) tles from suspension after playa flooding. Rosamond Calif. (34°50'N, 118°5'W) Motts (1969) INTRODUCTION North Panamint Calif. (36°20'N, 117°23'W) Motts (1969) The sliding stones of Racetrack Playa in Drinkwater Calif. (35°30'N, 116°33'W) Harold Ericsson Death Valley National Monument, (unpub. data) California, and the tracks they leave on this (34°53'N, 117°46'W) Win. Frazier smooth, normally dry lake bed have at- Small playa, Edwards Calif. Air Force Base (unpub. data) tracted much public and considerable scien- tific attention (McAllister and Agnew, Unnamed playa north Calif. (35°05'N, 116°26'W) Lyle Hoag 1948; Anonymous, 1952; L. G. Kirk, of Afton (unpub. data) Geological Society of America Bulletin, v. 87, p. 1704-1717, 21 figs., December 1976, Doc. no. 61205. 1704 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/12/1704/3418325/i0016-7606-87-12-1704.pdf by guest on 26 September 2021 SLIDING STONES, RACETRACK PLAYA, CALIFORNIA 1705 3S°40' Figure 1. Map showing access routes to Racetrack Playa. Peak at 1,730 m lies just 1.37 km off the west play a edge (Fig. 2). The surrounding bedrock is principally Paleozoic carbonates and Mesozoic intrusives (McAllister, • 1956). Racetrack Playa is bordered mostly by Figure 2. Physical bouldery alluvial fans backed by steep bed- setting map, elevations in metres; feet in pa- rock slopes (Fig. 3), but at its south end, a rentheses. large ridge of Cambrian dolomite rises abruptly from the playa margin (Fig. 4). Near its northern end, there are two bed- rock islands; the larger, The Grandstand, is of coarse porphyritic quartz monzonite, the Cottonwood Mountains (Fig. 1). Usual stricted by prohibitive signs and a ditch and the smaller is a knob of Paleozoic access is by way of a rough but maintained bulldozed in 1969 along the west margin. limestone. The proximate bouldery fans dirt road extending 42 km south from Monitored stones closest to the west playa and steep rock slopes provide the abundant Ubehebe Crater. Shorter access from the edge have suffered some tourist disturb- rock fragments resting on the playa surface. south can be gained, in proper season, by ance, but stones farther east have not been Cambrian dolomite comes from the south- the secondary Hunter Mountain road via molested. Total data losses are less than 10 shore rock ridge, syenite from coarse fans Jackass Spring, Harris Hill, Hidden Valley, percent. along the southeast and southwest margins, Lost Burro Gap, and Tea Kettle Junction This area receives rain and snow in and quartz monzonite from east- and west- (Fig. 1), generally transversable by a sturdy winter and occasional thunder showers in side fans farther north. Porphyritic quartz 2-wheel-drive vehicle. summer for an estimated annual precipita- monzonite is supplied by The Grandstand Tourists' visits to the playa are numer- tion of 7 to 10 cm. As much as 30 cm of add by northernmost west-side fans. ous, owing to National Monument public- snow has been seen on the playa surface Racetrack Playa is at the western border ity and keen interest in the sliding stones. (D. W. Carney, unpub. data), and freezing of Death Valley National Monument and is The playa surface was formerly disturbed temperatures are frequently attained at separated from northern Death Valley by by vehicular traffic, but that is now re- night in winter and spring. Winds are Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/12/1704/3418325/i0016-7606-87-12-1704.pdf by guest on 26 September 2021 1706 SHARP AND CAREY Figure 3. Looking north, local wet area and standing water along east shore with large projecting fan beyond. Dark bedrock island, The Grandstand, at arrow in distance, May 18, 1973. strong and reasonably frequent. Local ficial 2 cm contains the following per- scabby surface (Fig. 5). The clay chips pile topographic configurations may enhance centages: 24 fine sand, 41 silt, and 35 clay. up around bushes at the playa margin to velocity by channeling winds, particularly An inference that the northern end is 5 cm form small clay mounds. Thus, a significant from the south-southwest quadrant. The higher (Stanley, 1955, p. 1333) was fraction of the finest clay accumulates Ubehebe Peak topographic quadrangle confirmed by complete flooding in early around the playa margin. The clays of this (1:62,500; 1951) covers the area. Its geol- October 1974 that, under windless condi- playa are lower in montmorillonite and ogy has been mapped by McAllister (1956). tions, resulted in 5.5 to 7 cm of water near higher in illite than the average Mojave Although stones have moved on essen- the south end and only 0.5 to 1 cm over the Desert playa (Droeste, 1961). Algal depos- tially all parts of the playa, this study fo- northern part. Much of the playa surface its laid down from water standing a week cused on the southern sector, where stones displays a regular pattern of polygonal or more on the playa are also at least partly and tracks are most abundant. This was a mudcracks (Fig. 5) mostly 5 to 10 cm removed by the wind when dry. Material small-scale operation, personally funded, across, which survives wetting as new cracks exposed after removal of the top clay layer and resources to establish instruments for develop, largely along traces of older contains significant silt and fine sand.