[3] The park encompasses the caldera of Crater Lake, a remnant of Mount Mazama, a destroyed volcano, and the surrounding hills and forests.

The impressive average depth of this volcanic lake is due to the nearly symmetrical 4,000-foot-deep (1,200 m) caldera formed 7,700 years ago during the violent climactic eruptions and subsequent collapse of Mount Mazama and the relatively moist climate that is typical of the crest of the Cascade Range.

As stated in the foundation document:[5] Crater Lake National Park forever preserves Crater Lake, scenic landscapes, volcanic features, and unique ecological and cultural heritage, and fosters understanding and appreciation through enjoyment, education, and inspiration.Volcanic activity in this area is fed by subduction off the coast of Oregon as the Juan de Fuca Plate slips below the North American Plate (see plate tectonics).

Heat and compression generated by this movement has created a mountain chain topped by a series of volcanoes, which together are called the Cascade Range.

About 400,000 years ago, Mount Mazama began its existence in much the same way as the other mountains of the High Cascades, as overlapping shield volcanoes.

There continues to be debate as to whether these minor volcanoes and vents were parasitic to Mazama's magma chamber and system or if they were related to background Oregon Cascade volcanism.

[6] The eruptive period that decapitated Mazama also laid waste to much of the greater Crater Lake area and deposited ash as far east as the northwest corner of what is now Yellowstone National Park, as far south as central Nevada, and as far north as southern British Columbia.

Measurements at park headquarters, 6,475 feet (1,974 m) above sea level, show that snow falls more often here than at any other long-term weather station in Oregon.

Winter, which typically begins at the park in September and runs through June, includes an average of 101 days with measurable snowfall.

Mammals that are residents of this national park are Canadian lynxes, bobcats, beavers, chipmunks, pronghorns, foxes, squirrels, porcupines, black bears, coyotes, pika, badgers, deer, elk, muskrats, and martens.

[citation needed] Local Native Americans witnessed the collapse of Mount Mazama and kept the event alive in their legends.

One ancient legend of the Klamath people closely parallels the geologic story which emerges from today's scientific research.

A trio of gold prospectors—John Wesley Hillman, Henry Klippel, and Isaac Skeeters—were the first American prospectors to visit the lake.

William Gladstone Steel devoted his life and fortune to the establishment and management of a national park at Crater Lake.

In his efforts to bring recognition to the park, he participated in lake surveys that provided scientific support.

The party carried the Cleetwood, a half-ton survey boat, up the steep slopes of the mountain then lowered it to the lake.

From the stern of the Cleetwood, a piece of pipe on the end of a spool of piano wire sounded the depth of the lake at 168 different points.

Partly based on data from the expedition and lobbying from Steel and others, Crater Lake National Park was established May 22, 1902, by President Theodore Roosevelt.

The park is open to travel from late June or July 1 for as long as snow does not block the roads, generally until October.

On a clear day, visibility from the summit exceeds 100 miles (160 km), and one can, in a single view, take in the entire caldera.

Heavy snowfalls in this park during the fall, winter, and spring months force many road and trail closures, including the popular Rim Drive, which is generally completely open from July to October and partially open in some other months, such as May, June, and November.

The trail is the only one that accesses the shoreline of the lake, descending 656 feet (200 m) from the Cleetwood Cove parking lot.

First opened during the summer of 1960, the trail is 1.1 mi (1.8 km) long with an 11% grade that rates it as a strenuous route on the return trip.

A dock with concessionaire boats facilitates tours around the lake with a stop at Wizard Island for dropping off and picking up passengers.

The trailhead is located east of the Crater Lake Lodge and gains approximately 1,000 feet (300 m) of elevation.