There are a couple of reasons for the street name. One theory claims that it is named after the large rock in the state of Montana. A second theory is a reference to Rockstar's sexual humor; a Beaver is slang for pussy or vagina. Head is slang for giving someone oral sex. Combine those words to make Beaverhead and it implies someone giving oral sex to a vagina.
This is the spawnpoint in the Multiplayer Party Mode.
||Flathead Road||n/b toward Bridger Street|
s/b toward Manzano Road
||Big Horn Drive||e/b toward Owl Creek Avenue|
||Cassiar Avenue||s/b toward Big Horn Drive|
||Sacramento Avenue||e/b toward Bridger Street|
w/b toward Franklin Avenue