Выражение встречается в следующем контексте:
Ok, perhaps not a screaming downhill but it gets pretty wild when you are flying over loose rocks and gravel at 25 MPH. This section of trail is towards the top of the first good downhill. As you can see the grade isn't very steep, however it's easy to get up to high speeds quickly and when you hit a patch of loose stuff like I am about to in the photo you can lose control in a hurry. One thing not to do in the sections of loose rock is panic brake.

Мелкие камушки и песчаник, что-ли?

Заранее спасибо.