 Because of erosion phenomena during the previous Ice Age, the San Joaquin Hills are not one continuous mountain range, but instead are bisected by numerous water gaps cut by rivers flowing southwest from the Santa Ana Mountains.In the north, Newport Bay was formed by the Santa Ana River switching its course to the south, cutting across the northern part of the range.Laguna Canyon was formed by San Diego Creek, but eventually the larger creek changed course and left a wind gap through the hills.