CogKnoSys

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Physical

Lewis River

The Lewis River is a tributary of the Columbia River, about 95 miles long, that drains part of the Cascade Range in southwestern Washington.

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The idea

The Lewis River is a river in southwestern Washington that flows into the Columbia River. A smaller river that feeds a bigger one in this way is called a tributary, and big rivers usually collect water from many of them. The Lewis drains part of the Cascade Range, and its drainage basin covers about 1,046 square miles. A drainage basin is the whole area of land where rainfall and melting snow eventually run downhill into one particular river.

The river starts high on the west side of Mount Adams in the Cascades. It flows generally southwest through Gifford Pinchot National Forest and passes south of Mount St. Helens. Farther down, it forms the border between Cowlitz County to the north and Clark County to the south. Near its mouth, the East Fork Lewis River joins it. The river then enters the Columbia opposite St. Helens, Oregon, about 15 miles north of Vancouver, Washington.

Many people assume the river honors the famous explorer Meriwether Lewis, but that is a common misunderstanding. It was named for A. Lee Lewis, an early pioneer who made his home near the mouth of the river. Long before European settlers arrived, a number of Native American tribes were the first inhabitants of the valley it drains.

Check yourself

Question 1 of 3

Who was the Lewis River named after?

Pick one. The first pick counts.

Composition

what it's made of

  • Main river — The main Lewis, sometimes called the North Fork, which forms the line between Clark and Cowlitz counties.
  • East Fork — A branch that flows west from Lookout Mountain and splits Clark County in half.
  • Dams and reservoirs — Swift Dam, Yale Dam and Merwin Dam, which form Swift Reservoir, Yale Lake and Lake Merwin.
  • Horseshoe Lake — A lake in Woodland that was once a looping bend, or oxbow, of the North Fork.

Connection

how it relates

Under Lower Columbia Rivers and Waterways

In place

  1. Mount St. Helensstrength 70 of 100

    The Lewis River flows past the south side of Mount St. Helens.

  2. Gifford Pinchot National Foreststrength 70 of 100

    The river flows southwest through Gifford Pinchot National Forest.

  3. St. Helens, Oregonstrength 50 of 100

    The river's mouth lies across the Columbia from St. Helens, Oregon.

Cause and effect

  1. Electrical Energystrength 60 of 100

    The Lewis River's water is held back by dams on its North Fork to make hydroelectricity.

Related

  1. Cowlitz Indian Tribestrength 50 of 100

    A village about 5 miles up the Lewis was first home to Cowlitz people.

Change

how and why it evolves

Past
In 1792 William Robert Broughton passed the river's mouth while exploring the Columbia and named it Rushleigh's River.
Now
Today Swift, Yale and Merwin dams hold back the North Fork in its middle course for hydroelectricity and flood control.
Next
The river will likely keep supplying power and flood control, while people work to balance those uses with the health of its fish and forests.

Knowledge you can walk. Read the idea, then step up, across or down.

Lewis River

The Lewis River is a tributary of the Columbia River, about 95 miles long, that drains part of the Cascade Range in southwestern Washington.

See it on the map

Learn, discuss, create, buy or invest

The idea

The Lewis River is a river in southwestern Washington that flows into the Columbia River. A smaller river that feeds a bigger one in this way is called a tributary, and big rivers usually collect water from many of them. The Lewis drains part of the Cascade Range, and its drainage basin covers about 1,046 square miles. A drainage basin is the whole area of land where rainfall and melting snow eventually run downhill into one particular river.

The river starts high on the west side of Mount Adams in the Cascades. It flows generally southwest through Gifford Pinchot National Forest and passes south of Mount St. Helens. Farther down, it forms the border between Cowlitz County to the north and Clark County to the south. Near its mouth, the East Fork Lewis River joins it. The river then enters the Columbia opposite St. Helens, Oregon, about 15 miles north of Vancouver, Washington.

Many people assume the river honors the famous explorer Meriwether Lewis, but that is a common misunderstanding. It was named for A. Lee Lewis, an early pioneer who made his home near the mouth of the river. Long before European settlers arrived, a number of Native American tribes were the first inhabitants of the valley it drains.

Check yourself

3 quick questions, instant feedback.