Executive Summary

On January 28, 2021, a portion of scenic Highway 1 was eroded at Mile Marker 30 just south of Esalen, California, and north of Lucia, California. This closure of Highway 1 resulted in complete closure of the highway at that location and a detour of 158.5 mi (255 km) for travelers. Rat Creek runs up toward Dolan Ridge for about 1.6 mi (2.5 km) to about elevation 3,018 ft (920 m) above sea level. Water from Rat Creek flowed over Highway 1 and initiated embankment erosion on the downslope side of the pavement. The surface flow-induced erosion washed both lanes and some of the surrounding embankment material into the Pacific Ocean about 133 ft (122 m) below. This is not the first time that Highway 1 has been closed because of mudslides or debris flows. Data analysis of the aerial, terrestrial, and historical data suggests that the failure of Highway 1 at the Rat Creek drainage crossing was caused by inadequate drainage capacity.