The "West Gates" are part of the Tom Bradley Int'l Terminal, which is stoooopidly referred to as T-B by most airlines' sites. It makes no sense in an airport with T 1 through T8, but TB right at the end of the horseshoe. The West Gates are accessed through underground tunnel from the main part of TB. I've not arrived/departed from the West Gates, but I'd expect that they're set up for arrivals that can be routed right into the terminal (for domestic and pre-clearance arrivals) or on a sterile path to CBP.