The major part of the landslide consists of severely broken rubble. Individual rock fragments appear to be from the middle and upper units of the Altamira Shale, consisting of tuffaceous and silty shale. Fractured blocks of diatomaceous shale are found on the south slope of Blakesley HIll. Individual fragments of chert and cherty shale are found throughout the slide, though they are more abundant west of Portuguese Canyon. At the toe of the slide, between Inspiration Point and Portuguese Point, are weathered boulders of basalt.