Spaceborne radar image shows the Pinacate Volcanic Field in the state of Sonora, Mexico, about 150 93 miles southeast of Yuma, Arizona. The United States/Mexico border runs across the upper right corner of the image. The larger circular craters seen in the image are a type of volcano known as a "maar", which erupts violently when rising magma encounters groundwater, producing highly pressurized steam that powers explosive eruptions. The highest elevations in the volcanic field, about 4000 feet, occur in the "shield volcano" structure shown in bright white, occupying most of the left half of the image. Numerous cinder cones dot the flanks of the shield. The yellow patches to the right of center are newer, rough-textured lava flows that strongly reflect the long wavelength radar signals. Along the left edge of the image are sand dunes of the Gran Desierto. The dark areas are smooth sand and the brighter brown and purple areas have vegetation on the surface. Radar data provide a unique means to study the different types of lava flows and wind-blown sands. Image was acquired by SIR-C/X-SAR onboard the Endeavour on April 18, 1994.