A ravine usually starts below the ridge and continues down hilluntil it meets either flat land or a larger creek, river, or dam. They are created by water errosion and can be thought of as small canyons. They are usually narrow but can be very wide or open even (kind of like a quarry in a hill side).

The highest side of a gully that I know of (just dirt, not stone) is near the Nishnabotna River in Western Iowa and it has a verticle side 130 feet tall. The loess soil in Western Iowa forms spectacular gullies very quickly on the slope but the verticle sides ofthe gullies are quite stable.

I think gullies are sometimes called arroyos in the Southwest.

Bob