Quicksand is really not any special kind of sand, it is actually a condition that is happening to a patch of sand. There is an insistent flow of water beneath the surface, often an underground spring, that agitates the grains of sand, weakening them and lifting the grains apart. Each grain of sand is surrounded by a thin film of water and as they lose friction with each other, the solid mass breaks asunder. The water is not strong enough, however, to completely disperse the sand and the resultant soupy pool therefore can look like solid ground. Although the condition is most familiar in sand, any soil can become 'quick'.
Quicksand is found most anywhere water and sand mix every day.
Good places to find quicksand are on ocean coasts, near sandy creek beds and area of sand over an impervious clay substructure. Another good place to find quicksand is in hilly country with abundant caves and underground springs lurking beneath. The desert country of the southwest is such a place and, since there is often no apparent source of water nearby, the unexpected quicksand was a natural to catch the devious fancy of a Hollywood screenwriter. But unlike the bottomless pits of doom depicted in American westerns, most patches of quicksand are only a few inches to several feet deep. And quicksand does not pull its victim down to lethal depths like a deranged Hoover.