The Gulf of California ( also named as the Sea of Cortez or Sea of CortÃ s ; and nearby is known in the Spanish language as Mar de CortÃ s or Mar Bermejo or Golfo de California ) is a area of water that is inbetween the Baja California Peninsula and Mexican mainland . The Gulf of California ( also known as the Sea of Cortez or Sea of CortÃ s or Vermilion Sea ; locally known in the Spanish language as Mar de CortÃ s or Mar Bermejo or Golfo de California ) is a body of water that separates the Baja California Peninsula from the Mexican mainland .