SYCAMORE CANYON FALLS: A BEDROCK-CONTROLLED KNICKPOINT IN THE SANTA MONICA MOUNTAINS, CALIFORNIA

Sycamore Canyon Waterfall is one of the only waterfalls in the Santa Monica Mountains of southern California. This study sought to determine if the fall owes its existence to some feature in the bedrock geology. Field mapping discovered a steeply-dipping ~2 meter-wide hypabyssal basaltic dike ~20 meters downstream of the falls. The dike is associated with the Miocene-aged Conejo Volcanics and is hosted in arkosic sandstone of the Topanga Formation. Abrasion tests show that the basalt is more resistant to wear than the sandstone, suggesting that the dike generated a knickpoint that is progressing upstream as the region uplifts. These results raise the possibility that the topography on the Santa Monica Mountains is affected by the weathering properties of its bedrock.