Evidence gathered by expeditions of the University of California’s Scripps Institution of Oceanography during the International Geophysical Year suggests that the East Pacific Rise is one of the largest physical structures on earth. It runs in a sickle-shaped curve from near New Zealand 8,000 miles to the coast of Mexico. There its crest disappears from the maps, unless, as some now think, it underlies the western part of the North American continent. If so, then a previously described shoal area off the coast of Canada, reaching almost to Alaska, can be considered the northernmost end of the crest of the Rise. This would bring the total length to about 10,000 miles. Although the crest lifts itself two miles above the floor of the Pacific it still lies one and a half miles below the ocean surface, except where volcanic islands, such as Easter, thrust upward atop the bulge of the Rise.