Dendrophycus, originally described as the imprint of a marine alga of uncertain affinities, has long been suspect and is now generally considered to be a rill-mark. Several structures identical to Dendrophycus have been seen along creek banks in Wyoming and Colorado. These structures were observed to form as flood waters surged against the bank and eroded a modified dendritic pattern. The requirements for formation are: steep slope, semi-consolidated silt or fine sand, standing water, and surging currents. These conditions occur in marine and paralic settings, as well as fluvial. Because thestructure is inorganic, the term dendritic surge marks is suggested.