The Canadian River is the longest tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Arkansas River

Arkansas River

The Arkansas River is a major tributary of the Mississippi River. The Arkansas generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's initial basin starts in the Western United States in Colorado, specifically the Arkansas...

. It is about 906 miles (1,458.1 km) long, starting in Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

 and traveling through New Mexico

New Mexico

New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, the Texas Panhandle

Texas Panhandle

The Texas Panhandle is a region of the U.S. state of Texas consisting of the northernmost 26 counties in the state. The panhandle is a rectangular area bordered by New Mexico to the west and Oklahoma to the north and east...

, and most of Oklahoma

Oklahoma

Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...

.

The Canadian is sometimes referred to as the South Canadian River to differentiate it from the North Canadian River

North Canadian River

The North Canadian River is a tributary of the Canadian River, approximately long, that flows through New Mexico, Texas and Oklahoma in the United States....

 that flows into it.
The river rises on the east side of the Sangre de Cristo Mountains

Sangre de Cristo Mountains

The Sangre de Cristo Mountains are the southernmost subrange of the Rocky Mountains. They are located in southern Colorado and northern New Mexico in the United States...

, at approximately 9600 ft (2,926.1 m), in remote southwestern Las Animas County, Colorado

Las Animas County, Colorado

Las Animas County has the largest area of the 64 counties of the State of Colorado of the United States. Las Animas County takes its name from the Mexican Spanish name of the Purgatoire River, originally called El Río de las Ánimas Perdidas en Purgatorio, which means "River of the Lost Souls in...

, approximately 1.5 mi (2.5 km) north of the New Mexico

New Mexico

New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

 border.