North Polar Sand Sea
A vast sea of dark dunes, sculpted by the wind into long lines, surrounds the northern polar cap of Mars. The dunes appear to be basaltic sand. Taken altogether, the dune field covers 679,000 square kilometers (260,000 square miles) - about as extensive as all Texas.
In any event, winds blowing past the hill have deflected around it, breaking the dunes' linear pattern into barchans and creating narrower lines of smaller dunes on the downwind side (lower left).