White Sands, 275 square miles of gypsum.

Field guide ◆ White Sands

Plan the trip.

White Sands National Park sits in the Tularosa Basin of southern New Mexico — 275 square miles of pure white gypsum sand dunes, the world's largest such dunefield. The sand is white because it's gypsum (calcium sulfate, the stuff of drywall) rather than silica, and it's the result of an evaporated ancient sea bed combined with a closed basin and wind.

For a focused trip: Drive Dunes Drive at sunset (8 miles, paved-then-gypsum-packed). Hike the Alkali Flat Trail (5 miles, follow the orange poles — the dunes shift). Sled the white sands using a plastic sled (rentable at the visitor center). Stay through twilight — the white turns blue then pink as the sun drops.

Best window: October to April. Summer surface temperatures hit 150°F on the dunes. Backcountry camping is allowed but the park is also a weapons-test range adjacent to White Sands Missile Range (closures during testing — check before you go).