I don't know. But according to the game guide there are no behemoths. The Behemoths were exclusive to the east coast and there aren't that many as it takes many years for them to reach that size.
The west coast strain of super mutants is very different from the east. On the west coast the mutants don't continue mutating, they don't eat people, they by and large have the intelligence of small children[and often even the temperament] though a few actually gain increased intelligence or no impact at all. The east coast mutants are monsters, the west coast mutants are still people.