Deadfall

With the final word of the spell you call into being a huge tower of logs and branches. It collapses to the ground with a roar, crushing creatures beneath its weight.

(Spell Compendium, p. 59)

Originally posted on D&D tools

Conjuration (Creation)
Level: Druid 8,
Components: V, S,
Casting Time: 1 standard action
Range: Long (400 ft. + 40 ft./level)
Effect: Mass of dead wood forming in a cylinder (20-ft. radius, 40 ft. high); see text
Duration: Instantaneous; see text
Saving Throw: Reflex partial; see text
Spell Resistance: No

Pick a point on the ground as the center of the radius and bottom of the cylinder. Deadfall creates a tangled mass of huge branches, logs, and fallen trees on the ground. The deadfall immediately collapses in on itself with terrific force and noise. Creatures and objects in the area take 1d6 points of damage per caster level (maximum 20d6). In addition, creatures in the area must succeed on a Reflex save or be knocked prone.

Once you cast the spell, a considerable volume of dead wood remains behind. This pile of brush is 5 feet high, with a 20 foot radius, and it counts as dense rubble (DMG 90).