Sediments of the bays, shelf, and slope off Guatemala and Honduras consist of terrigenous detrital minerals and rock fragments carried onto the shelf by rivers or eroded from the coast or shelf bottom, skeletal debris of marine organisms, and authigenic minerals formed on the sea floor. The predominant sediment fraction is clay in bay and slope samples; sand in inner-shelf samples; and sand, silt, or clay in outer-shelf samples. Five sedimentary facies named on the basis of predominant organisms and sediment size in samples are distinguished: molluscan-barnacle clayey facies, molluscan-bryozoan sandy facies, algal sand facies, molluscan-foraminiferal lutitic facies, and planktonic clayey facies. The molluscan-barnacle clayey facies is present on the shelf edge and slope a water depths of 50 to more than 500 fm. The other facies are found on the shelf. Carbonate sediments in samples at depths of 16.5-50 fm and sand and gravel in samples at depths of 12-15 fm are predominantly relict deposits formed at a time of lower sea level. The relict sand deposits of the shelf probably are being diluted now by recent clays from coastal rivers.