Much of the coastal topography around the bay is very steep, rising almost immediately from the shoreline to elevations of . Like the other major channels of the Bras d'Or Lake (St. Patricks, Great Bras d'Or, Little Bras d'Or and St. Andrews), East Bay has a northeast - southwest orientation. Rifting and regional tectonic plate movements some 360 million years ago formed this directional series of small fault bounded basins between highlands of resistant crystalline rock. The northern shoreline suggests that the bay is largely underlain by Carboniferous Windsor Group sedimentary rocks, principally shale, sandstone and gypsum. The southern shoreline is generally the elongated block of Precambrian rocks known as the East Bay Hills, composed of volcanic deposits of the Fourchu Group (ash and lava interleaved with marine sediments) and earlier Paleozoic era intrusive granite and quartzite. This is some of the oldest surficial geology visible around the Bras d'Or Lake, yet soft Windsor Group rocks form a narrow band along the bay's southern shore and extend out as the lake floor.