The Colorado River, measured in length and drainage area, is the largest river wholly in Texas. (The Brazos drainage basin extends into New Mexico.) It rises in intermittent draws in northeastern Dawson County (at 32°41' N, 101°44' W), flows generally southeastward for 600 miles across Borden, Scurry, Mitchell, Coke, and Runnels counties, and forms all or parts of the county lines between Coleman and Concho, Coleman and McCulloch, Brown and McCulloch, Brown and San Saba, Mills and San Saba, Lampasas and San Saba, Burnet and San Saba, and Burnet and Llano counties, before it bends to the east across southern Burnet County and continues its southeastern course across Travis, Bastrop, Fayette, Colorado, Wharton, and Matagorda counties to its mouth, on Matagorda Bay (at 28°36' N, 95°59' W). Its drainage area is 39,900 square miles, and its runoff reaches a volume of more than 2 million acre-feet near the Gulf. The major towns along the stream are Austin, Lamesa, Colorado City, Robert Lee, Ballinger, Paint Rock, Marble Falls, Bastrop, Smithville, La Grange, Columbus, Wharton, Bay City, and Matagorda. Important reservoirs on the Colorado include Lake Colorado City, Lake J. B. Thomas, Buchanan Lake, Inks Lake, Lake Lyndon B. Johnson, Lake Travis, and Town Lake in Austin.
The Colorado River is probably the one called Kanahatino by Indians of the Caddoan linguistic family and Pashohono by some of the other Indian groups. It has also been identified as the stream that Juan Domínguez de Mendoza and Nicolás López called San Clemente in 1684, and as the one René Robert Cavalier, Sieur de La Salle, named La Sablonnière ("Sand-Pit") in 1687. The name Colorado, Spanish for "red," is evidently a misnomer, for the water of the stream is clear and always has been, according to the earliest records of historians. Most authorities agree, however, that the name Colorado was first applied by Alonso De León in 1690, not to the present stream but to the Brazos, and there is considerable evidence to support the theory that the names of the two streams were interchanged during the period of Spanish exploration. The present names, however, were well established before the end of Spanish Texas. Other historic associations along the Colorado include the river's use as a route inland by early colonists, including several of the Old Three Hundred who settled on its banks; the establishment of Austin as the seat of government in 1839; and the fact that in 1844, when both England and France were working to prevent the annexation of Texas by the United States, the British minister in Mexico secured a written avowal from Antonio López de Santa Anna to recognize the independence of Texas with the Colorado River as its boundary.
The river flows across the rolling prairie near San Saba County, enters the more rugged Hill Country and the Llano basin, and passes through a series of canyons before it issues from the Balcones Escarpment at Austin. Above Austin the lands along the Colorado are generally rough, but below Austin the river traverses the flat, alluvial bottoms of the Coastal Plain, an important agricultural area. Principal tributaries of the river include the Pedernales, Llano, San Saba, and Concho rivers and Pecan Bayou, the most westerly "bayou" in the nation. With the exception of the bayou, the tributaries flow into the river from the Edwards Plateau and are spring-fed. Although the Colorado has a relatively small annual run-off with relation to its watershed, it has presented some of the most serious drainage problems in Texas. Early in the nineteenth century its slow current caused the formation of a raft, or log jam, which gradually grew upstream so that the river was navigable in 1839 for only ten miles above its mouth. By 1858 the situation in Matagorda and Wharton counties had become so bad that the state appropriated funds for the construction of a new channel around the raft. The United States Army Corps of Engineers opened the channel in the mid-1800s, but since it was not maintained the raft filled it up. Teamsters unloaded vessels above the raft and carried the cargo to other teams that loaded it on other boats for shipment to Galveston and other Gulf ports. Shallow-draught vessels were at times able to ascend the Colorado to Austin.
After the Civil War the Colorado ceased to be a factor in transportation. The delta that developed after removal of the log jam, beginning in 1925, reached across Matagorda Bay as far as Matagorda Peninsula by 1936; that year a channel was dredged through the new delta from the Gulf of Mexico to the town of Matagorda, thus forcing the river to deposit its flotsam and sediment directly into the Gulf. With removal of the raft, the community of Matagorda, formerly a major Texas seaport, gradually became landlocked. The present Caney Creek channel was the channel of the Colorado until about a thousand years ago, when the river cut into a wide estuary in the present Caney Creek area and redirected its flow to the west.
The need for a steady flow of water to irrigate rice farms in Wharton and Matagorda counties, combined with the necessity for flood-control measures, has presented more recent challenges. These have been met largely by the construction of Lake Travis and Lake Buchanan. Three smaller reservoirs in Burnet County-Inks, Johnson, and Marble Falls-produce power from water running over the Buchanan Dam spillway. The dam at Lake Austin, which is largely filled with silt, produces power from water flowing from the lakes above. Town Lake, a recreation site that divides north and south Austin, is the last impoundment in this section of the river; Town Lake and the lakes above Austin are known as the Highland Lakes. Conservation and use of the Colorado are overseen by three agencies established by the state legislature, the Lower, Central, and Upper Colorado River authorities, and formerly the Colorado River Municipal Water District.