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.
Balanus glandula, the boring polychaete Polydora (Boccardia) proboscidea, and the boring clams Petricola pholadiformis (introduced), Zirfaea pilsbryi, and Platyodon cancellatus (an uncommon, native species). Pockets of gravel over hardpan (often wetted by runoff) are characterized by the amphipod Paramoera bousfieldi n.sp. Many of the species found on bedrock and riprap nearby may also occur here.
Goose Point (Willapa Bay), Alki Point, north of Shilshole Bay, Lincoln Park, Richmond Beach.
Kozloff, 1983; Hedgpeth and Obrebski, 1981; R. Anderson, C. Staude unpubl. data.