The Making of a Perfect Racetrack at the Bonneville Salt Flats

Abstract

THE STORY OF THE SALT It is a unique experience being out on the salt at the Bonneville Salt Flats. The sun seems a bit too bright as light reflects off the cubic halite crystals that cover the stark saline ground (Figure 1). There is a sense of isolation and vastness with the curvature of the earth visible on the horizon. There is a profound silence. The only sound on some hot, dry days is the crackling of halite crystals as they precipitate from shallow brines. Void of any macro flora or fauna, the salt flat ecosystem is only apparent in thin layers of bright green or pink halite below the surface, or the insects that are trapped in the growing salt. Wagon tracks left when the ill-fated Donner Party became bogged in the sediment in 1846 reportedly remained visible in the salt for over 90 years; a vivid reminder of the dangers of this harsh landscape. Car tire tracks have long since replaced wagon tracks. Each year in the late summer, when the salt crust permits, the silence of the salt explodes with the roars of racing motors. Land speed records were set on the Bonneville Salt Flats through the 20th century; it is a landscape intricately linked with U.S. car culture. The final season of Mad Men shows the protagonist, Don Draper, speeding recklessly through the night across the salt flats: a symbol of his fragile freedom and the endless possibility of the West. The landscape has called dreamers and innovators, daring them to push the limits of human speed. The geology of the Bonneville Salt Flats tells a story of landscape change on a range of temporal scales—from tectonic processes over millennia to seasonal fluctuations to even shorter timescale events that change the surface with a single storm event or week of sunshine. Humans have come to value this relict landscape, but the Bonneville Salt Flats is an active and dynamic system, changing continuously in response to rain, wind, evaporation, and groundwater flux. These are all factors over which humans have little direct control. The impacts of long term, natural, geological processes morph together with landscape responses to human presence— a century of racing, mining, and recreation; and now, additionally, mitigation and adaptation of diverse stakeholder communities reacting to the everchanging conditions. The Bonneville Salt Flats (BSF) is a perennial salt pan that spans over ~75 km adjacent to the Utah–Nevada border (Figure 2). The extension of the Basin and Range lays the tectonic framework for the development of interbasinal playas, like the Bonneville Salt Flats, where groundwater flowpaths focus discharge and concentrate solutes in springs rimming playa boundaries (Gardner and Heilweil, 2014). On glacial-interglacial time scales, the impact of Pleistocene Lake Bonneville and a cold and wet climate regime are evidenced by a series of tufatraced shorelines stepping down the southeast face of the Silver Island Mountains, bounding the salt flats to the northwest, and by the vast lacustrine playa surface that blankets the Great Salt Lake Desert. The Great Salt Lake and BSF are both remnants of Pleistocene Lake Bonneville which drained at the end of the last glacial maximum and desiccated over the last ~13,000 years (Oviatt, 2015). As regional climate warmed and dried through the Holocene, the pluvial lakes of the Pleistocene glaciations disappeared, leaving both a sedimentary and hydrological footprint, as much of the groundwater in the Basin and Range is dated to ~20 ka— Bonneville water (Gardner and Heilweil, 2014). Isostatic rebound of the Bonneville lake basin (Crittenden, 1963; Oviatt, 2015) and hypothesized neotectonic faulting along the northwestern edge of the salt flats moved the West Desert’s low point from further east to the western edge of the basin at the modern BSF, where a wedge of salts concentrated and precipitated over thousands of years. On human time scales, cycles of flooding, drying, and automobile racing punctuate the seasonal transitions in the landscape. This combination of geologic and hydrologic circumstances led to a thin (<2 m) accumulation of saline chemical sediments in the westernmost surface of the Great The Making of a Perfect Racetrack at the Bonneville Salt Flats