fractal brownian motion terrain

i have created a terrain using fractal brownian motion. i have also created camera movement by translating and rotating the terrain to look like movement. The problem is that i want to attach the camera to the terrain so that it looks as if you are running along terrain, but because the points on the terrain are odd i am having trouble attaching the camera to the terrain because i cannot find the y point at any given x or z. any ideas or addvice.

what about (simplified) collision detection ?
create a vector (0,-1,0) and use triangle-ray intersection tests with your (pregenerated)landscape mesh.
(if you want to do it fast, i would suggest a using fast culling like quad- and octrees.)