Chad's Gap was first referenced in Episode 6 of BBLiveShow. Someone named "Timbo" called in and asked Brian and Mike how to get to Chad's Gap from the bottom of Alta. He also claimed to have a friend who "hit it" and broke his ankles.
It was one of the show's first "WTF!?" moments.
The call starts at 41 minutes into the recording of Episode 6.
Location of Chad's Gap
Chad's Gap is apparently a location in Utah. Although it is not an established ski area, it seems to be a fairly legendary place for extreme skiing. It is located just north of Alta.