Range is Short, no SR. For 1 round/level you create 1 square of caltrops that behave exactly as their mundane caltrop brethen. For every 2 caster levels over 1, you get an additional square full of caltropian fun (to a max of 5, just like Magic Missile), and every caltrop created by the spell get a +1 bonus to hit (capping at +4, too)
It's specified that piling caltrops in the same square doesn't do any good. Difficult to believe as it is, there's such thing as too many caltrops.