Geology
The dominant geological feature in the Santiago Creek watershed are the Santa Ana Mountains. The northern portion of the mountains, which Santiago Creek drains, is composed of rocks from the pre-Triassic to the Quaternary (251–2.6 MYA). These rocks consist primarily of slate, sandstone, conglomerate, limestone, and other sedimentary rocks. 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.
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