Inaccurate?

Rain of Spines

(Complete Mage)

Conjuration (Creation) [Earth]
Level: Wu Jen 4 (metal),
Components: V, S,
Casting Time: 1 standard action
Range: Medium (100 ft. + 10 ft./level)
Area: Cylinder (5-ft. radius, 20 ft. high)
Duration: Instantaneous
Saving Throw: Reflex partial
Spell Resistance: No

With a shout, you call down a rain of spines upon your foes, piercing their flesh and pinning them to the floor.
You cause a veritable storm of small, piercing metallic projectiles to rain from the air.
This spell deals 6d6 points of damage to each creature in the area.
In addition, each creature in the area is knocked prone and immobilized by spines pinning it to the floor.
A successful Reflex save halves the damage and negates the secondary effect.
A creature immobilized by spines is considered entangled and can't move from its space for 1 round per caster level; a DC 20 grapple check or Escape Artist check allows it to break free and end the secondary effect.