You searched for: Place Sister Rocks 7.5' quad. North Coast. Marsh on north side of Hwy 101, 1.0 km northwest of Humboldt Road, about 2.1 km southeast of Crescent City, north-northeast side of the marsh. Remove constraint Place: Sister Rocks 7.5' quad. North Coast. Marsh on north side of Hwy 101, 1.0 km northwest of Humboldt Road, about 2.1 km southeast of Crescent City, north-northeast side of the marsh.