Page:Popular Science Monthly Volume 69.djvu/295

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the Pacific, each earthquake rift follows the line of an old fault, and the original break goes back to the mountain-making periods of Tertiary times. The California earthquake of 1906 follows the axis of an ancient break, the 'Portolá-Tomales fault' or 'San Andreas fault,' first studied, so far as I know, by Dr. John C. Branner in 1892. In this fault hundreds of thousands of earthquakes, large and small, have