The Bonneville flood had catastrophic effects along the Snake River in what is now Idaho, but the influence of the flood can also be detected within the lake basin where a distinctive layer of sediment was deposited. The Bonneville flood bed can be identified in many surface exposures below the Provo shoreline and in sediment cores. The flood bed is characterized by an abrupt contact at its base between massive marl, which was deposited in the deepest water of Lake Bonneville, and finely laminated or ripple-laminated sandy marl, which was deposited by bottom currents during the flood. In places the Bonneville flood bed is composed of reworked ostracode shells. The contact at the top of the flood bed is transitional to massive marl that was deposited in the lake floor during Provo time. The flood bed is best developed and most obvious in straits between partially submerged mountain ranges or in places where bottom currents were strong as lake water flowed toward its outlet at Red Rock Pass. Because the Bonneville flood bed was deposited in less than a year, it is useful as a well-dated (~18,000 yr ago) stratigraphic marker within the Bonneville deposits.