Question: Which  international border is San Ysidro Port of Entry at  
Sentence (from "San Ysidro, San Diego"): It neighbors Otay Mesa West to the north, Otay Mesa to the east, and Nestor and the Tijuana River Valley to the west; together these communities form South San Diego, a pene-exclave of the City of San Diego, thus making it possible to travel (by water) between central San Diego and South San Diego without ever leaving the city limits.
Relevant evidence: No