Question: Williamsport, Arizona is on the bank of one of the  principal rivers of the Southwestern United States and northern Mexico that is how long
Context: Verbena menthifolia is a species of verbena known by the common name mint-leaved vervain or mint vervain.  It is native to the southwestern United States and northern Mexico, where it occurs in many types of open, dry habitat such as desert scrub.  This perennial herb produces one or more rough-haired, erect stems up to about 75 centimeters in maximum height.  The hairy leaves are a few centimeters long and are divided near the base into a few narrow lobes which have serrated edges.  The inflorescence is made up of one to three narrow, erect spikes of flowers up to 30 centimeters long.  The flowers are spaced, not densely packed on the slender spike.  Each flower has a small purple corolla 2 or 3 millimeters wide. Lupinus concinnus is a species of lupine known by the common name Bajada lupine.  It is native to the southwestern United States from California to Texas, and northern Mexico, where it is known from many types of habitat.  This is a hairy erect or decumbent annual herb with a stem growing 10 to 30 centimeters long.  Each small palmate leaf is made up of 5 to 9 leaflets up to 3 centimeters long and under a centimeter wide, sometimes narrow and linear in shape.  The inflorescence is a dense spiral of flowers, with some flowers also appearing in leaf axils lower on the plant.  Each flower is 5 to 12 millimeters long and purple, pink, or nearly white in color.  The fruit is a hairy legume pod around a centimeter long. The cane cholla (or walking stick cholla, tree cholla, chainlink cactus, etc.) (Cylindropuntia imbricata) is a cactus found in the Southwestern United States and northern Mexico, including some cooler regions in comparison to many other cacti.  It occurs primarily in the arid regions of the Southwestern United States in the states of Oklahoma, Texas, New Mexico, Arizona, Colorado, and Nevada.  It is often conspicuous because of its shrubby or even tree-like size, its silhouette, and its long-lasting yellowish fruits. Carex spissa is a species of sedge known by the common name San Diego sedge.  It is native to the southwestern United States in California, Arizona, and New Mexico, and far northern Mexico.  It grows in wet places such as seeps and streambanks, sometimes on serpentine soils.  This sedge looks somewhat like a cattail.  It produces angled stems easily exceeding a meter in height surrounded by leathery green to reddish leaves up to about 1.2 meters long.  The inflorescence is up to 80 centimeters long, with many long reddish brown flower spikes, each holding up to 300 developing fruits. Ericameria laricifolia is a North American species of flowering shrub in the daisy family known by the common name turpentine bush, or turpentine-brush.  It is native to the southwestern United States (Arizona, New Mexico, western Texas, southwestern Utah, southern Nevada, southeastern California) and northern Mexico (Chihuahua). Nolina microcarpa is a species of flowering plant in the asparagus family known by the common names sacahuista and palmilla.  Like other species of "Nolina", it may be called beargrass.  It is native to northern Mexico and the southwestern United States in Arizona and New Mexico.  It does occur in the southwestern corner of Utah, where it has a limited distribution on Navajo Sandstone, but reports of it occurring in Texas may be in error. Williamsport, is a former mining town and present day ghost town, on the bank of the Colorado River in La Paz County, Arizona. Aztlanolagus is an extinct monotypic genus of rabbit that lived during the Quaternary of the Southern to Southwestern United States and northern Mexico.  Aztlanolagus agilis is currently the only recognized species, though differences among recovered fossils suggest that there may have been other species.  The generic name refers to Aztlán, the legendary place of origin of the Nahua peoples as recorded in the mythological accounts of the Aztecs and other Nahua groups.  By some traditions, this legendary locale is placed in the border regions of the Southwestern United States and adjacent northern Mexico. The Rio Grande ( or ; Spanish: Río Bravo del Norte , ] or simply Río Bravo) is one of the principal rivers in the southwest United States and northern Mexico (the other being the Colorado River).  The Rio Grande begins in south-central Colorado in the United States and flows to the Gulf of Mexico.  Along the way, it forms part of the Mexico–United States border.  According to the International Boundary and Water Commission, its total length was 1896 mi in the late 1980s, though course shifts occasionally result in length changes.  Depending on how it is measured, the Rio Grande is either the fourth- or fifth-longest river system in North America. The Colorado River is one of the principal rivers of the Southwestern United States and northern Mexico (the other being the Rio Grande).  The 1450 mi river drains an expansive, arid watershed that encompasses parts of seven U.S. and two Mexican states.  Starting in the central Rocky Mountains in the U.S., the river flows generally southwest across the Colorado Plateau and through the Grand Canyon before reaching Lake Mead on the Arizona–Nevada border, where it turns south toward the international border.  After entering Mexico, the Colorado approaches the mostly dry Colorado River Delta at the tip of the Gulf of California between Baja California and Sonora.
Answer: 1450 mi