Low tide bares a wide expanse of sand patterns and tidepools at Coast Guard Beach.
The ocean also invaded parts of the land, creating estuaries and embayments at the mouths of these glacial valleys, such as those at Pamet Harbor and Blackfish Creek. Several of the Cape’s “salt ponds,” such as the one in Eastham below the visitor center, were originally freshwater kettle ponds that have been breached by the rising sea.
As Cape Cod was being smoothed, slimmed, and invaded by the rising sea, it was also being lengthened. Like a sculptor working in clay, the ocean currents took much of the eroded cliff material and, carrying it both north and south, created the elaborate forms of the barrier beaches, barrier islands, and sand hooks that give the Outer Cape its characteristic filigreed coastline. Monomoy Island, North Beach, Nauset Beach, Coast Guard Beach, and Jeremy Point are some of the more prominent of these post-glacial landforms, enclosing such important estuaries as Pleasant Bay, Nauset Harbor, and Wellfleet Harbor. Among the more unusual formations are the tombolos of outer Wellfleet Harbor: the series of short sand beaches that connect Bound Brook, Griffin, Great Beach Hill, and Great Islands.
Of all these sea-spawned parts of Cape Cod, however, the most impressive and extensive is undoubtedly the Provincetown Hook. These 3,000 acres of dunes at the northern tip of the Cape form a broad recurved spit of sand that encloses Provincetown Harbor, one of the finest deepwater harbors on the East Coast and the initial port for the Mayflower Pilgrims in 1620. Some oceanographers believe that the hook began to form as much as 6,000 years ago and has built up in a series of roughly parallel ridges, or dune lines, widening out into the ocean.
In the protected bays and inlets behind these elongating fingers of barrier beaches and islands, salt marshes—one of the Cape’s most characteristic and important ecosystems—began to form 4,000 to 6,000 years ago. Composed of a few species of salt-tolerant grasses, primarily the stalky cord grass (Spartina alterniflora) and the finer salt hay (Spartina patens), these green salt meadows of the sea built slowly on the accumulating sediment deposited in protected areas of water by the tides and land runoff. Gradually, as the sea rose relative to the land, the marshes raised and spread themselves on a platform of their own decay, forming thick beds of peat underneath them. As the climate continued to warm, the Cape’s woodlands evolved from boreal forests to the mixed pine-oak woodlands we see today.
Pitch pine is the most common tree on Cape Cod and the only species of native pine that grows in the National Seashore. It survives on well drained glacial sediments and stable sand dunes and is very fire resistant. In this stand on Great Island, the undergrowth is primarily bearberry.
As the Cape’s post-glacial environment grew more diverse and complex, so did the culture of the people living on it. The first Native Americans on Cape Cod are now thought to have arrived at least 9,000 years ago. By the late Archaic Period, starting about 5,000 years ago, local Indian groups had developed a seasonal pattern of movement based on multiple resources. During the warmer months they settled on the shores of bays, marshes, and fish runs, trapping birds and collecting herring and shellfish. In winter they retreated inland to the more protected forested shores of ponds and other wetlands.
By the beginning of the Woodland Period, about 2,500 years ago, Indian settlements had grown even more numerous, larger, and more sedentary. About 800 years ago agriculture and a variety of new materials and tools had been introduced. One of the most important of these “tools” was fire; with it the Cape’s Native Americans changed the face of the land.