The Colorado River “Basin” includes the entire watershed of the Colorado River.

• The Upper “Basin” is the portion of the total watershed that drains into the Colorado River upstream of Lees Ferry.
• The Lower “Basin” is the portion of the total watershed that drains into the Colorado River downstream of Lees Ferry.

The States that make up the Colorado River Basin are divided by the Colorado River Compact into the:

• Upper Division: Colorado, New Mexico, Wyoming and Utah
• Lower Division: Arizona, California and Nevada.

Each “Division” is defined by state boundaries.

Each “Basin” is defined by watershed boundaries.

For example, looking at the Basin map, you can see that portions of Arizona are in the green Upper “Basin,” despite Arizona being a Lower Division state; and parts of New Mexico are in the yellow Lower “Basin,” despite being in an Upper Division state.