Raycast not working on terrain

So I have this terrain mesh:

And I'm trying to get a raycast from the player to the terrain, so I can see where on the terrain he's looking. I tested it on a simple flat plane, and that works fine, but when I try the terrain mesh it doesn't seem to hit anything. After a little bit of testing, it seems like the raycast doesn't work on a mesh with a lot of small vertices, because when I made this mesh with only a few larger vertices it works fine.

Am I doing something wrong, or is what I want simply not possible?