 The uplift of the Santa Ana Mountains began approximately 5.5 million years ago along the Elsinore Fault Zone, which extends north from near its namesake Lake Elsinore area.Before the latter 19th century, Santiago Creek and its tributaries were free flowing perennial streams spilling out of Santa Ana Mountains canyons onto the broad, alluvial floodplain.The creek wound on the plain for the rest of its course to its confluence with the Santa Ana River.