There is a parking area on NH-1A on the north side of Great Boars Head.

As described by geologist Charles H. Hitchcock in the Geology of New Hampshire, Great Boar’s Head is a lenticular moraine or drumlin, an elongated deposit left by a glacier, perhaps one million years ago. Hitchcock suggested that some of the rocks found around the Head may have come from as far away as the Ossipee Mountains, about 60 miles northwest of Hampton Beach.

Albert N. Dow of Exeter, who had a summer place on the Head, attempted to determine the original size of Boar’s Head. In a series of articles printed in the [Exeter] News-Letter in 1925, Dow estimated that originally the drumlin was 2,400 feet wide and extended, in a southeast direction, 3,300 feet into the ocean. Dow based his conclusions on the arrangement of large rocks surrounding Boar’s Head left by the erosion of soil over the centuries. Much of this eroded material was washed by the sea into a natural bar that connects the Head to the mainland. Dow believed that the present northwesterly slope of the Head was original and unchanged by nature. Based on conversations with many old-timers, Dow said he thought the point of the Head had receded about 28 feet between 1875 and 1905, and while storms from the north meant that the north side of the Head was eroding twice as fast as the south side, it appeared that sea action was not the only cause for the erosion. Great storms had a serious impact, but Dow believed that the spring thaws, when the clay ran in muddy streams from around the rocks on the slopes, were probably the most active form of erosion.

According to Lewis Nudd, who ran the Eagle House (now the Century House), the erosion also removed the Head’s namesake. Nudd, who died at age 90 in 1923, told Head residents that when he was a boy, there was a profile view of a boar’s head seen from the south side. Part of this profile was created by a large rock that protruded from the steep bank. Before the turn of the century, Nudd said, the rock fell into the sea, removing forever the profile of the boar’s head.