The river rises in the Kalmiopsis Wilderness, northwest of Chetco Peak at the junction of the Oregon Coast Range and the Klamath Mountains.

Several explorers, including Sir Francis Drake, George Vancouver, and Jedediah Smith, visited the region between the 16th and 19th centuries, and found the Chetco people inhabiting the area.

[4] It flows between Bosley Butte to the north and Mount Emily to the south; the latter is the impact site of one of only four bombs known to have been dropped in the continental United States by an enemy aircraft.

[4] The United States Geological Survey monitors the flow of the Chetco River at a stream gauge at RM 10.7 (RK 17.2), which is 6.8 miles (11 km) northeast of Brookings.

[2][7] The increase in temperature is caused by the geography of the region; cool air funnels down the Chetco River valley from the Siskiyou and Coast ranges, gradually heating up before eventually reaching Brookings as a warm wind.

[2] The Cascadia earthquake of 1700—estimated at 8.7–9.2 on the moment magnitude scale—caused a tsunami to sweep across California, Oregon, Washington, and British Columbia, reaching Japan the next day.

It was produced when the entire Cascadia subduction zone, about 680 miles (1,100 km) long, slipped approximately 66 feet (20 m) in a megathrust event.

[2] The Columbus Day Storm of 1962 brought devastating winds to nearly all of Oregon; nearby Port Orford recorded gusts exceeding 190 miles per hour (310 km/h).

Manzanita, hazelnut, vine maple, western skunk cabbage, and multiple species of berries and grasses make up the understory.

[2] The world's northernmost redwood grove is located near the south bank of the Chetco at RM 15 (RK 24), about 8 miles (10 km) north of the California border.

Prior to logging, the massive trees created their own microclimate by capturing moisture from fog, and also by the immense amount of shade they produced.

[18] Mammals such as American black bears, black-tailed deer, bobcats, ring-tailed cats, and gray foxes are common inhabitants of this region.

Coastal cutthroat trout can be found all around the watershed; some migrate to the ocean, while others live in the river and its tributaries year round.

[24] The Chetco River flows through the ancient Klamath Mountain terrane, which is between 400 and 100 million years old, the oldest rocks in Oregon.

[25] The Klamath microcontinent was originally located beneath the ocean near southern California before separating hundreds of millions of years ago.

[26] Plate tectonics pushed the microcontinent north, and bits of granite, sea floor sediment, subduction zones, and coral reefs gradually accreted into small islands.

[25][26] Between 212 and 170 million years ago, a massive volcanic arc erupted on the Klamath microcontinent, binding the islands together in a single block.

The process was strong enough to force sedimentary rocks deep into the Earth's crust, melting them into large plutons of granite, which rose slowly to the surface.

[27] Shortly after, a large portion of sea floor was thrust over the older Klamath terranes; much of it is still visible atop Vulcan and Chetco peaks.

[28][30][31] The mountainous terrain of the Chetco River watershed was created approximately 130 million years ago when the microcontinent collided with the much larger North American continent.

The first inhabitants were perhaps ancestors of the Chetco Indians and other Native American tribes, themselves descendants of the first humans who traveled across the Bering land bridge from Siberia over 10,000 years ago.

[36] In June 1828 Jedediah Smith and his company of fur traders camped on the south bank of the river near a Native American village.

[36][37] Between 1853 and 1855, many Native Americans were killed and their villages destroyed in skirmishes occurring around the same time as the nearby Rogue River Wars.

In 1932, the Isaac Lee Patterson Bridge was completed over the Rogue River to the north, connecting the region to the rest of the Oregon coast.

[45] In 1964, the United States Congress set aside over 80,000 acres (32,000 ha) of the eastern Chetco River watershed and surrounding regions to create the Kalmiopsis Wilderness.

[13] In 2002, 45 acres (18 ha) of land on the Little Chetco River were sold to Washington real estate developer David Rutan, only several months after the Biscuit Fire tore through the region.

Curry County officials soon stated that the camp violated zoning and sanitation laws, but inspections were stymied because of the area's inaccessibility.

High turbidity levels in the Chetco River watershed are usually caused by landslides, various forms of erosion, and plugged road culverts.

[2] Fishing, four-wheel driving, swimming, boating, camping, sightseeing, and picnicking are the primary recreational activities in the watershed.

[52] Chetco Point Park, located near the wharf, has several fire rings and picnic tables, as well as views of the river, the Pacific Ocean, and the Port of Brookings Harbor.