The Slide Mountain Ocean was an ancient ocean that existed between the Intermontane Islands and North America in the Triassic time beginning around 245 million years ago. Its name origin comes from the Slide Mountain Terrane, a region made of rocks from the floor of the ancient ocean. There was a subduction zone on the Slide Mountain Oceans floor called the Intermontane Trench where the Intermontane Plate was being subducted under North America. The floor of the Slide Mountain Ocean was pushed up onto the ancient margin of North America.
The namesake of the Slide Mountain Ocean is Slide Mountain in the Canadian province of British Columbia, lying on the north side of the Quesnel River.