Its the offshore area - out into the pacific - I don't know exactly how far it extends.. at least to the islands - I did find this definition of it:
The Continental Borderland is an offshore geomorphic
region extending from Point Conception in southern Cali-fornia
to the Vizcaż“no Peninsula in Baja California, Mexico,
that contrasts markedly with the nearly flat 30- to 50-km
wide continental shelf off most of the Californias. It is a 250-
km-wide zone of bathymetric lows (basins and troughs) and
highs (ridges, banks, knolls, and islands) that separate the
coast from the abyssal floor of the Pacific Ocean. The Patton
Escarpment to the north and the Cedros Deep to the south
(Moore, 1969) delineate its western limit.