During April and May of 1959, 26 seismic refraction stations were completed in the Gulf of California. In the shallow Northern Gulf province the crust of the earth consists of four layers--1.5 km of unconsolidated sediments with a velocity of 2.1 km/sec, 2.0 km of semiconsolidated sediments with a velocity of 4.1 km/sec, 4.3 km of basement material with a velocity of 5.4 km/sec, and a main crustal layer with a velocity of 6.7 km/sec. The total thickness of the crust is not well determined but appears to be about 25 km. In the central and southern sections of the Gulf only two layers can be resolved--a 1.3 km layer of unconsolidated material, and 6.2 km of material with a velocity of 5.8 km/sec. The subcrustal material has an average velocity of 7.8 km/sec and lies at a de th of 9.3 km. South of the Gulf proper the crust can be resolved into three layers--0.4 km of unconsolidated sediments, a 1.3 km layer with an average velocity of 5.5 km/sec, and a 4.3 km third layer with an average velocity of 6.7 km/sec. The upper mantle lies at an average depth of 8.9 km, and has a velocity of 7.7 km/sec. It is concluded that the northern portion of the Gulf of California has a structure similar to the continental borderland off Southern California, and that the southern section has a structure similar to the East Pacific Rise.