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+! EA NPS Farm 10.900-9 WE (am) United States Department of the Interior National Park Service National Register of Historic Places Continuation Sheet OUn Approve? No. 1024-00f S Section number� Page I Indian River Narrows Cultural Resource District Geographical Data The State of Florida Indian River County The Indian River Narrows Cultural Resource District is located upon Orchid Island, a barrier island that makes up the easternmost portion of the Atlantic Coastal Ridge (ACR) physiographic province. It is separated from Florida's peninsular mainland by the Indian River lagoon to its west and bounded by the St, Lucie Inlet to the south, by the Sebastian Inlet t the north, and by the Atlantic Ocean to the east. The ACR is a series of relict sandy beach ridges and bars which formed parallel to the Atlantic Ocean through wave, wind and current action as the sea level has risen and fallen over time. The narrowness and close proximity of the ACR, which comprises the mainland dune ridges and Orchid Island, to the Atlantic Ocean in Indian River County has led geologists to surmise that this area is one of the geologically most recent oceanic shores to be formed along the state's Atlantic coast (White 1970:85). Providing geologic stability to Orchid Island against the constant erosional activity of winds, waves, and currents is the Anastasia Formation, The Anastasia Formation is an extensive deposit of coquina rock extending from St. Augustine southward for about 150 miles to northern Palm Beach County. Coquina is a rocky mineral comprised of whole or broken shell and quartz sand (in varying proportions) typically cemented together by calcium carbonate or iron oxide (Cooke and Mossum 1929:191-203) that is the remains of ancient beach deposits (Scott 1997:60, 66). In places the formation also has substantial deposits of marl. The Anastasia Formation, which formed during the Pleistocene period, can be seen at points along the shore and is the only rocky coast on the eastern side of the state north ofthe Florida Kcys. By its imnwbilit-�, It anchors the barrier islands and their high primary durst -.s a0 helps to prevent overwashing and landward migration of sediment (Davis 1997:158). Covering the Anastasia Formation is a geologically thin band of Holocene sediments that form the present beach, dune, marsh, and lagoon sediments along the Atlantic shore (Scott 1997:67). These more recently formed parts of the present coastline are being gradually covered by a constant rise in sea level. The sea level along the Atlantic coast has been risitig at approximately 1 cm. every 25 years for the last 3,000 years, a decrease from the rate of l cm. every 4 years that occurred between 6000-1000 B.C. and the early Holocene rate of approximately I cm. per year (Davis 1997:157). Because of the narrowness and steepness or the Continental Shelf adjacent to Florida's Atlantic coast and the relatively high mean annual wave heights, 70 cm. here versus 10-25 cm. on the state's Gulf Coast (Davis 1197:156), ccrribistcd with a tisc In swa k;vc Ll the shoreline or Orchid island is subject to dytiamic georuorphic changes. At various times the inlet on the northern end of the island has been naturally formed and sealed in several other locations.