Part of quicksand’s menace is its deceptive resemblance to solid ground. Underneath the firm-looking crust–which can be sand, silt, clay, or other grainy soils–is a slurry of soft, wet, quivering earth nicknamed “jelly mud.” Unlike regular mud, which compresses to support weight, this quagmire collapses easily. The water that saturates the soil (and creates the muck) often flows underground  and isn’t visible on the surface, though quicksand also can develop beneath shallow pools.
Quicksand requires only soil and water–in the right amounts. When the ground is dry, the constant friction between individual sand grains creates a stable, interlocking foundation. But when the ground becomes saturated, water molecules push apart the grains, reducing the intergranular friction and the soil’s weight-bearing ability. The soil becomes “quick” when the water pressure supporting the sand equals or surpasses the weight of the sand,  creating a floating suspension with the consistency of wet concrete that will trap your leg, and won’t let it go.
Salt makes quicksand less stable, especially in clay-like soil, by reducing the elasticity between sand grains. As a result, people generally sink deeper in ground saturated with saltwater than with freshwater. Salt eroded from sandstone canyon walls in southern Utah generates an ideal environment for quicksand when it accumulates in silt-filled arroyos.
Quicksand typically forms along the inside curves of rivers and sand washes, [a] where natural springs or runoff saturate an area of soft sediments. Other common spots include marshes, coastlines, and riverbanks. Quicksand can be persistent in canyons fed by spring water, and can appear rapidly after floods, spring run-off, or during low tide [b]. Post-flood conditions can be particularly dangerous, says Mike Salamacha, a BLM ranger in the Arizona/Utah Paria Canyon Vermilion Cliffs Wilderness. “Everything is wet, and you can’t tell where the quicksand is until you walk on it.” Quicksand can develop from Alaska to Florida, but hotspots include the marshy coasts of the Southeast, such as Florida and the Carolinas, and the canyons of southern Utah, northern Arizona, and New Mexico.
Don’t struggle. Since the human body is half as dense as quicksand, you won’t sink much below your knees, or to your waist under rare circumstances. Fighting the suctionlike pull can be exhausting–especially if you’re hauling a heavy pack–and can cause you to sink deeper by making the solution more fluid. To extract yourself, stay calm and lean backwards to spread out your weight while backstroking to firmer ground. Kick your legs slowly to loosen the surrounding sand, and move deliberately toward the edge. Ditch your pack if necessary. In areas prone to quicksand, like canyons and marshes, use a stick or trekking pole to probe the surface.