Treasure Island is a drumstick barrier that has been completely developed by human activity during the past half century. The island has been reasonably stable except at the south end where Blind Pass has migrated about 2 km to the south over the past 100 years or so. Changes at Blind Pass are linked to the formation of Johns Pass (to the north) by a hurricane in 1848. Much of the tidal prism from Boca Ciega Pass (now Blind Pass) was captured by this newly formed inlet, causing it to diminish in size, become unstable, and migrate to the south (Barnard, 1998). After stabilization of Blind Pass in 1936, there has been a continual problem due to infilling from southerly littoral drift along the barrier.

The island transect includes the southern part of Treasure Island, the northern part of Long Key (Yale, 1997) and across the back-barrier area up Bear Creek on the mainland. The basal unit recovered in the cores taken on or adjacent to the barrier islands contains muddy, shelly sand that is interpreted as representing a low-energy marine environment that may or may not have been protected by a barrier island. Channel deposits characterized by shelly sand are present under both islands and represent environments associated with the migration of Blind Pass (FitzGerald, 1995). Nearshore, beach, and dune deposits characterize the barriers themselves, with some indications of reworked washover deposits. Cores taken from Bear Creek on the mainland show a sequence of late Pleistocene to Holocene radiocarbon dates (see cross section below) that suggest a conformable transition across the Pleistocene/Holocene boundary at the landwardmost portion of the transect.