dark parts of the two-toned rocks, the height of the largest of the bright (light-toned) rocks, and the perched rocks would suggest local deflation of 5 to 60 cm. Thus, there must have been previous deposition on this order. The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundleadjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials. References and NotesDuring the first few Mars solar days (sols) (1) of operations, we determined the landed location in inertial coordinates by analyzing Spiritto-Earth two-way X-band Doppler transmissions and two passes of ultrahigh-frequency two-way Doppler between Spirit and the Mars Odyssey orbiter. The equivalent location in the International Astronomical Union (IAU) 2000 body-centered reference frame is 14.571892°S, 175.47848°E. The location with respect to surface features was derived by the correlation of hills and craters observed in images taken by the Pancam, the Entry Descent and Landing (EDL) Camera, and the Mars Orbital Camera.On the basis of these analyses, the landing site is located at 14.5692°S, 175.4729°E in IAU 2000 coordinates, ϳ300 m north-northwest of the radiometric solution. This offset is consistent with the map tie errors between inertially derived coordinate systems and those derived from image-based coverage of the planet. Localization experiments during traverses focused on systematic acquisition of forwardand backward-looking overlapping images, onboard inertial measurement unit (IMU) observations to derive rover tilt, and tracking the number of wheel turns to provide wheel-based odometry. These observations were employed in a least-squares bundle adjustment to solve for the position and orientation of Spirit in local Cartesian coordinates at discrete locations during traverses (Fig. 1 and Plate 14). In addition, measurements of differential rocker and bogie angles in the suspension system, together with IMU data, were used to reconstruct the elevation of each wheel at a 2-to 8-Hz sample rate relative to the start of each traverse (Fig. 1).Localization results were extracted for 33 traverse segments from the Columbia Memori-

The location of the Opportunity landing site was determined to better than 10-m absolute accuracy from analyses of radio tracking data. We determined Rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images. Topographic profiles generated from rover data show that the plains are very smooth from meter- to centimeter-length scales, consistent with analyses of orbital observations. Solar cell output decreased because of the deposition of airborne dust on the panels. The lack of dust-covered surfaces on Meridiani Planum indicates that high velocity winds must remove this material on a continuing basis. The low mechanical strength of the evaporitic rocks as determined from grinding experiments, and the abundance of coarse-grained surface particles argue for differential erosion of Meridiani Planum.