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This three-dimensional perspective view illustrates the subsurface geology of Vancouver and the Fraser Valley. Knowledge of geology at depth comes from drill holes and geophysical surveys. Because this information is limited, the interpretation shown here is speculative. The diagram shows a deep basin in granitic rock beneath the Fraser Valley. Sandstone filling this basin is more than 4 km thick near Tsawwassen but pinches out at the edges of the basin. The sandstone, in turn, is overlain by Ice Age sediments up to 1 km thick. Generally thinner modern sediments are limited to low-lying areas (Fraser delta) and the Strait of Georgia, where they are currently being deposited. Faults (fractures along which there has been movement) offset bedrock and control some linear features such as Sumas Prairie. These faults are not known to be active.