Simplify the following text for a Grade 8 native English-speaking person.
Original: Bitumen is a term used for natural deposits of oil `` tar '' - such as at the La Brea Tar Pits .
Simplified: Naturally occurring `` tar pits '' ( e.g. the La Brea Tar Pits in Los Angeles ) actually contain asphalt rather than tar . Tar sand deposits contain various mixtures of sand ( or rock ) with bitumen or heavy crude oil and not tar , as does the Tar Tunnel in Shropshire .