Thanks. I've hiked my share of hills, especially in geology-heaven, New Mexico (the 'land of ensandment'), and they can provide surprises around every turn -- canyons and collapses and deep rockslides, dikes and vents and salt pans on shoulders, house-sized rocks that crumble as they rolled downhill, dust traps, mineral deposits from springs and seepage, vertical and overhanging cliffs, cave mouths, ventifacts in narrow arroyos, even natural bridges. Some weird stuff makes the hair on the back of your neck stand up, especially if you can never get close enough to determine -- as usually the case -- it's an odd natural formation. Squyres hoped that the hills were leftovers from massive erosion that swept the floor of Gusev and left outflow deposits at one rim.