This image covers part of the central uplifted region of an unnamed crater in Phlegra Dorsa.
This complex crater is approximately 30 kilometers (about 18 miles) in diameter and is centered at 23 N latitude and 176 E longitude. The transition from a simple bowl-shaped crater to a complex crater exhibiting central peaks or pits, flat floors and terraced walls takes place in craters that are larger than about 8-10 kilometers (or roughly 5-6 miles) in diameter on Mars. Because the central uplifts of complex craters expose rocks and materials that originated deep below the surface, researchers can use these regions as possible “windows” to view the rocks beneath the surface.
A northeast-southwest linear valley or trough transects this region dividing the uplift in two. This valley, or lineation, may have resulted from processes occurring during the uplift event or subsequent to crater formation. When seen at HiRISE resolution the center of this valley seems to bisect what may be a small (less than a kilometer wide) central pit.
Written by: Shawn D. Hart and Ginny Gulick (3 February 2010)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_010888_2030
Image: NASA/JPL/University of Arizona