Field Investigation of Pluvial Features in Surprise Valley as Analogs for Pluvial Landforms on Mars

The presence of liquid water on the martian surface as localized, confined standing bodies of water needs to be considered and investigated. A field study of a paleo-pluvial lake was conducted April 14 to 19, 2008, in the southern end of Surprise Valley, which extends across the Nevada-California border. Distinct linear features that parallel the topographic contours of the ridges bounding the valley are evident in both remote sensing images and from the roadside. We collected 900 positional points along ten transect lines using a Trimble R8 Differential Global Positioning System (DGPS), tied to a published USGS reference elevation, which facilitates correlation of shoreline elevations to <0.5 m across the 8.5 km width of the valley. Each transect crossed a series of paleo-shorelines expressed as terraced benches along the valley walls. The morphologic expression of some shorelines can vary over horizontal distances <100 meters, likely influenced by variations in local bedrock and soil development, whereas some shorelines can be correlated around the entire southern end of Surprise Valley. Tufa accumulations on and around cobbles and boulders are very pronounced along at least two shorelines. The western valley wall has a steep slope with the highstand and tufa deposits comprising the most prominent shorelines. The eastern valley wall has a gentle slope with several shorelines, including the highstand and tufa shorelines. Student activities could involve mapping shorelines on satellite images, field identification of the lake highstand, interpretation of the asymmetric slopes of the valley walls, and identification and discussion oftufa. The data obtained from the investigation in Surprise Valley should be applicable as primary referents for evaluating the possibility of a pluvial origin for features observed inside some large impact crater basins on Mars.