Features That Illustrate the Glacial History Between
Fort Ebey State Park and Fort Casey State Park
Sherman Road/Cemetery Drive/Ebey's Prairie Trail. This route follows a north-south-oriented bluff above Ebey's Prairie. The slope down to the prairie is the face of a marine delta that was deposited by sediment-laden glacial melt water flowing into the shallow sea. As the streams entered the sea they dropped their sediments. The upland on the east side of Ebey's Prairie is also a delta left by retreating glaciers. At that time (about 13,000 years ago) sea level was at where you are standing on the top of the bluff. The sea floor was about 100 feet (30 meters) below you. The seafloor of that time is now 100 feet (30 meters) above present-day sea level.
Along the beach from Pondilla Lake to Ebey's Landing (4.3 miles/6.9 miles). The wave-cut cliffs above the beach expose about 250 feet (76 meters) of interbedded sand, gravel, and mixtures of sand and gravel. Most of these sediments were deposited at or below sea level by outwash from sub-glacial streams. Close to Partridge Point, 1.3 miles (2 kilometers) southeast along the beach is a kettle exposed in cross-section. The kettle was partly filled with wind-blown sand about 8000 years ago. The cliffs are being eroded by wave action and landslides and supply the sediment needed to maintain the beaches by longshore drift. 0. 6 miles (1 kilometer) northwest of Ebey's Landing is Perego's Lake, a brackish lagoon protected by a spit that is maintained by longshore drift of beach sediment.
Take a Break - Have a picnic or visit Historic Coupeville
If you are walking, continue down (east) along Highway 20 on the Kettles Trail, which will take you into Coupeville.
If you are driving, head north into Coupeville along Engle Road (turns into Main Street), where you will find a variety of good restaurants. In Coupeville, along Main Street, just south of Highway 20 and an elementary school, behind Coupeville Coffee is "Big Rock." "Big Rock" is a 22 foot (6.7 meter) tall glacial erratic boulder left by a retreating glacier. The erratic was probably plucked out of bedrock on Fidalgo Island, 13.5 miles (21.7 kilometers) north of Coupeville and carried to its present location. The rock is on private property and covered with English ivy (a less-than-desirable invasive plant).
Fort Casey State Park
Below the land surface, the seacliffs that border the Admiralty Inlet Preserve present a view of the interplay between deposition and erosion during several periods of glaciation (80-60 thousand years ago, 37 thousand years ago, and 21 thousand years ago). To complicate matters, those deposits have been crossed in several places by segments of the SE-NW-trending Southern Whidbey Fault Zone. Mostly buried by young glacial deposits, the Southern Whidbey Fault Zone has been defined mostly through geophysical surveys of the sea floor in Admiralty Inlet and Saratoga Passage.
Surface deposits in Fort Casey State Park are glaciomarine drift that was deposited on an earlier sea floor near the retreating ice front. Most of the plateau surface has been severely modified by the construction of Fort Casey. Deep trenches were dug for mortar emplacements, separated by embankments that hid the powder magazines. A man-made embankment that is above the western beach hid large artillery pieces.