Tectonic Edge

Oracle Text

T: Add C.

1, T, Sacrifice Tectonic Edge: Destroy target nonbasic land. Activate this ability only if an opponent controls four or more lands.

Card Rulings

3/1/2010 Tectonic Edge’s second ability checks how many lands an opponent controls only at the time you activate the ability.
3/1/2010 Assuming you can activate Tectonic Edge’s second ability, you can target any nonbasic land with it (not just one controlled by an opponent that controls four or more lands).