Estuarine, intertidal, hardpan, partly enclosed, eulittoral

Areas of hardpan are common in Puget Sound, yet few surveys have been done. Hardpan is resistant basal till, composed of poorly sorted but well compacted glacial deposits often including clays. Hardpan shelf habitat may be seen in the mid-low intertidal and often has pockets of sand overlying it. The hardpan tends to erode more readily than bedrock and thus does not harbor as many long-lived species, but does contain some unusual organisms such as boring clams and the other species that live in their burrows.