Uninterpreted seismic profile reveals several Holocene sand ridges with good basal Holocene reflections marking the top of Pre-Quaternary bedrock. These ridges are separated by 1-km-or-greater expanses of sea floor where sediment thickness decreases below the level of detection (approximately 0.5 m). Sand ridges are less than 2 to 3 m thick, corresponding with the higher-relief portions of the sand waves or ridges seen here. Somewhat better subbottom penetration shallower than the 20-m isobath reveals deformed bedrock strata typical of isolated shelf-valley structures found in the nearshore zone south of Tampa Bay (see transect #6 for example of shelf valley).