Ark Island is situated at the mouth of the Aniakchak River on the north shore of Aniakchak Bay and on the southeastern coast of the Alaska Peninsula, about 205 miles (330 km) southwest of Kodiak and 47 miles (75 km) northeast of Chignik, Alaska. The name for the island is unofficial and used locally, possibly referring to the splintered remains of a scow once used to maintain fish traps. Aniakchak River drains Surprise Lake in the caldera of Mount Aniakchak and flows generally southeast for about 36 miles (58 km) through Aniakchak National Monument and Preserve to Aniakchak Bay. The name of the river was first reported by Walter R. Smith and Arthur A. Baker of the U.S. Geological Survey who referred to the river as the largest stream on the Alaska Peninsula flowing toward the Gulf of Alaska. Three large bays on the Gulf of Alaska coast bordering Aniakchak National Monument and Preserve are the remnants of ancient volcanic craters. The two larger bays are Aniakchak Bay, Amber Bay to the north, and the smaller Kujulik Bay to the south. All have cinder-covered beaches between the sea and large freshwater lagoons. Ark Island may be a remnant of an ancient volcano composed of rocks belonging to the Meshik Volcanics from the early Oligocene and late Eocene that consist of basaltic volcanic rubble and basalt lava flows. Until about 3,650 years ago, Mount Aniakchak was an Aleutian Range stratovolcano with an elevation exceeding 7,000 feet (2134 m) and composed of basalt and dacite. The mountain then collapsed during a massive eruption that caused the loss of about 3,000 feet (914 m) of the upper mountain. The remainder of the mountain then collapsed leaving a relatively flat-floored, ash-filled basin or caldera that filled with water, and eventually, hydraulic pressure or overflow caused a breach of the caldera wall at a weak or low point. The result was a massive flood that created the great cleft through the caldera wall now known as The Gates. The most recent volcanic activity came in 1931 when an explosion of thousands of tons of ash was scattered up to 40 miles (64 km) away. This volcanic episode was documented by the geologist and Jesuit priest, Father Bernard Hubbard. His films, photographs, and descriptions provide an important benchmark for judging the rate of recovery of vegetation and the repopulation of animals in the caldera.

The Aniakchak River provides one of the best salmon spawning habitats on the Pacific coast of the Alaska Peninsula, and the north shore of Aniakchak Bay, just east of the river mouth, provides one of the most equable habitation sites in the area. The combination of fishing resources, a sheltered location, and the presence of freshwater has attracted humans to the area for thousands of years. This is one of the few known prehistoric sites on the central Alaska Peninsula. The archaeological record suggests that the entire central Alaska Peninsula was occupied, abandoned, and re-colonized numerous times, perhaps in response to recurrent catastrophic volcanism. Nothing is known of the people who lived in the area prior to the cataclysmic eruption of the Aniakchak stratovolcano, but it is unlikely that the region was uninhabited. The eruption, however, fundamentally altered the landscape and likely buried any pre-eruption evidence of human activity. Lands nearest the caldera were largely uninhabited for millennia and the Pacific coast was resettled between 1575 and 1655 AD. Historically this volcanic wasteland has formed the boundary between Aleut Unangan speakers in the southwest and Alutiiq Sugpiat speakers in the northeast. The narrow Alaska Peninsula, only 45 miles (72 km) across at Aniakchak, allows access to the distinctly different environments of the Bering Sea and Pacific coast and it is likely that trade and internecine conflicts regularly brought Native groups in contact. In 1783, the Russian Gregory Shelikhov subjugated the Alutiiq on Kodiak Island and founded the first non-Native settlement at Three Saints Bay. His fur trade empire then dominated economic and social life on the Alaska Peninsula. Russian fur traders conscripted Alutiiq people to hunt or trap puffins, sea otters, seals, and foxes first for the Shelikhov-Golikov Company and later for the Russian-American Company. In 1917, commercial fishing operations began at the mouth of the Aniakchak River when the Columbia River Packers Association established a series of fish traps. The company soon recognized that the bay offered some of the best trap sites on the Pacific coast of the Alaska Peninsula and as a result, the company operated traps in the bay for most of the next 30 years. In 1924, the company built a bunkhouse and stationed crews in a bunkhouse near the river mouth to guard the traps and maintain the operation.  In 1932, razor clams were discovered in Aniakchak Bay and a cannery was established that year which quickly depleted the clam population.

In 1978, Aniakchak National Monument was established by President Jimmy Carter under the Antiquities Act. The original monument covered 380,000 acres (150,000 ha) and did not include the area between the caldera and the coast. In 1980, the Alaska National Interest Lands Conservation Act was finally passed, establishing the unit as a national monument surrounded by a larger national preserve that extended to the coast on the south side of the peninsula. The national monument allows subsistence hunting by local residents in most areas and the national preserve allows both subsistence and sport hunting. The Aniakchak Bay Historic Landscape District surrounds the Aniakchak River from Aniakchak Crater to Aniakchak Bay. The Aniakchak River was designated a National Wild and Scenic River in 1980 by the U.S. Congress. The river is floatable in small to medium rafts and kayaks. From Surprise Lake in the caldera, the river flows about 1 mile (1.6 km) to The Gates, which is a narrow gorge in the caldera wall. It then plunges through 15 miles (24 km) of rocky rapids rated between Class II (medium) to IV (very difficult) on the International Scale of River Difficulty. Below the rapids, the rest of the river is rated Class I (easy). After 5 miles (8 km), the river slows and begins to meander toward Aniakchak Bay. In addition to rapids and low water temperatures, the area has notoriously bad weather with winds up to 100 miles per hour (160 kph) that can damage equipment and prevent airplanes from landing at the lake or on the bay. Brown bears are frequently seen along the river and near the bay where they scavenge for food. These factors plus the remoteness and isolation limit the number of visitations and Aniakchak is known as the least visited unit in the National Park system. Read more here and here. Explore more of Aniakchak here: