The park is located on the Alaska Peninsula, across from Kodiak Island, with headquarters in nearby King Salmon, about 290 miles (470 km) southwest of Anchorage.

The monument and surrounding lands became appreciated for their wide variety of wildlife, including an abundance of sockeye salmon and the brown bears that feed upon them.

Katmai occupies the Pacific Ocean side of the Alaska Peninsula, opposite Kodiak Island on the Shelikof Strait.

The park has been extensively altered by glaciation, both in the high lands where the mountains have been sculpted by glaciers, and in the lowlands where lakes have been excavated.

During that time about 0.7 cubic kilometers of material was erupted to form a new peak called Southwest Trident from the former site of a large fumarolic pit.

A large lava flow extends from the mountain to fill the upper part of Angle Creek's valley with about five cubic kilometers of material.

[20] Apart from steaming there has been no recent activity, but there was a large debris avalanche in 1912, probably associated with the eruption of Katmai, amounting to between 0.05 and 0.10 cubic kilometer in volume.

Activities at Katmai include hiking, backpacking, camping, backcountry skiing, fishing, kayaking, boat tours, and interpretive programs.

According to the United States Department of Agriculture, the Plant Hardiness zone at Brooks Falls at 92 feet (28 m) elevation is 3b with an average annual extreme minimum temperature of −30.9 °F (−34.9 °C).

Salmon enter the Naknek River drainage from Bristol Bay in June and July and spawn from August to October.

Common wildflowers that grow in the park include beachhead iris, nootka lupine, and woolly geranium.

[43] Prehistoric artifacts have been found dating to about 6,000 years before the present near the old Katmai village on the park's south coast.

Some of these, including sites "49 AF 3" near Kanatak and "49 MK 10", present clear evidence of habitation up to the 1912 eruption, but have not been investigated in detail.

[46] The National Geographic Society backed five expeditions to Katmai, beginning in 1915 with a trip to Kodiak Island and a short stay on the mainland.

The expedition, led by Robert Fiske Griggs, a botanist who was initially interested in the study of plant recolonization.

Griggs' follow-up expedition in 1916 discovered and named the Valley of Ten Thousand Smokes and found Novarupta.

At the same time, the Park Service became aware that Katmai was among the best habitat for grizzlies in Alaska, and that the monument should be expanded to protect them and the prolific salmon spawning grounds.

In 1931 President Herbert Hoover issued a proclamation expanding the monument under the Antiquities Act to 2,697,590 acres (1,091,680 ha), more than doubling it in size and creating the largest single Park Service unit.

Crucially, the expanded monument included the falls at Brooks Camp, while avoiding lands along the coast thought to have potential oil deposits.

In 1939 the United States Bureau of Fisheries established an encampment at the Brooks Lake outlet, having previously blasted out part of the falls in 1921.

At about the same time the Park Service became concerned about illegal trapping in the monument, asking the Alaska Fish and Game Commission to send wardens to patrol the area.

Several trappers were apprehended, and Park Service personnel visited the monument, sending back positive reports on the scenery and wildlife.

[48][49] In the 1990s a state game refuge, with 120,000 acres (49,000 ha) was established to the north of the sanctuary to protect Chenik Lake, which supported a smaller fish run, attracting bears.

The refuge and the expanded 128,000 acres (52,000 ha) sanctuary have remained closed to hunting, despite an unsuccessful 2005 attempt by Governor Frank Murkowski and again in 2007 by Sarah Palin's Board of Game.

The study identified 39 site that might become preserves or recreation lands, and it recommended that Katmai be expanded somewhat to the west and substantially to the north.

The boundary adjustments were amended to a westward expansion of 94,547 acres (38,262 ha) that President Lyndon B. Johnson signed in 1968, producing anger in Alaska.

To address these concerns, legislation was proposed to create national preserve lands that would confer protection while allowing regulated sport hunting.

Because a deadline was approaching for state selection of public lands, President Jimmy Carter used his authority under the Antiquities Act to expand Katmai by 1,370,000 acres (550,000 ha) on December 1, 1978, mainly on the northern side of the monument.

[55] The grounding of the oil tanker Exxon Valdez in Prince William Sound on March 24, 1989, produced extensive contamination of the Katmai coastline.

In early May, a variety of dredges and skimmer vessels were working in the Shelikof Strait, but 90% of the Katmai coastline was oiled.