New field observations, petrology, geochemistry, and ⁴⁰Ar/³⁹Ar geochronology are reported for the Scripps Dike, which crops out at the coast north of La Jolla, California. The northeast–southwest-trending and laterally discontinuous dike has a basaltic–trachyandesite bulk composition, with an emplacement age of 13.89 ± 0.13 Ma. Modeling of the dike composition indicates that it formed from 0.5 to 1.5% partial melting of a primitive mantle-type source, metasomatized by slab fluids, predominantly in the garnet stability field. The composition of the dike, including relatively high MgO (6.6 wt.%) and Sr/Y (~105), makes it akin to magnesian andesites in...