The Thickson Woods Great Horned Owls are not hard to find, but most of the time, finding it is hit and miss. The tree are well over 30ft tall, and the two are always there. Just a question of whether you manage to spot them or not. If you get down there in the spring around April/May, there's always lots of birders around, just ask. Most of the time, walk down to the bird sightings box, and look up high around that area, radius of approx 50ft.
Don't forget that they're very good at hiding/blending in.