In my experience, impressa, pylartes and obliqua (three of the four native eastern Colobopsis excluding Florida's riehlii) are generalists, nesting in just about any sort of twig, though I find many species nesting in hollows in White Ash trees from abandoned mississippiensis chambers. I typically find colonies 2 meters or higher off the ground, though I occasionally see nests lower on trees, particularly with a large mississippiensis satellite nest that was in some of the young twigs sprouting out of the base of the tree. Colonies of most species are typically restricted to dead portions of living trees, the exceptions being mississippiensis and occasionally obliqua, which I have seen nesting in still living portions of Ash limbs, likely overtaking the mississippiensis colony there before them. The plants I've seen these ants nesting in include Muscadine, White Ash, Flowering Dogwood, Fishpole Bamboo, Water Oak, Red Maple, Post Oak, Wild Blackberry and Groundsel. However, impressa (and by extension riehlii) is known to nest in dead portions of Red Mangroves in Florida. If you really want to find these ants, you'll certainly have to do some climbing, because they certainly do not nest close to the ground by any means, and climbing is typically the only viable method of colony collections. And heads up, once you find a nest, you might want to make sure there are no other nests nearby, as they are known to make multiple satellite nests as the colonies are surprisingly large.
