Massmorph

With this spell the caster causes 1d4+1 man-sized (or smaller) creatures per four caster levels to appear as if they are natural effects of the terrain (for example, trees in a forest, stalagmites in a cave, coral underwater, boulders in a cavern, etc.). All creatures to be affected must be within a 120' radius of the caster at the time the spell is cast. Only those creatures the caster wishes to hide are affected, and then only if they are willing to be concealed. The caster may include himself or herself among the affected creatures.

Those affected are thus concealed from other creatures passing through the area for so long as they remain still. If an affected creature chooses to move or attack, the illusion is dispelled for that creature, but those who remain still continue to be hidden. The caster may end the spell early if he or she wishes by speaking a single word. The illusion can also be ended by dispel magic.