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 (Lemhi Street is named for the Lemhi Pass in the Beaverhead Mountains, fitting the Western theme). 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