when did the europeans arrived?
1539
Southwestern United States
The first European intrusion into the region came from the south. In 1539, a Jesuit Franciscan named Marcos de Niza led an expedition from Mexico City which passed through eastern Arizona. 
where is the colorado river located on the map Southwestern United States and northern Mexico what are its tributaries? Gila River, Gunnison river, San Juan river, Green river, etc. who were the early settlers here? Spanish what kind of plants are found here? Creosote bush, saguaro cactus, and Joshua trees, etc. how has the environment been effected? Reduction in flow caused by dams, diversions, water for thermoelectric power stations, and evaporation losses from reservoirs – the latter of which consumes more than 15 percent of the river's natural runoff—has had severe ecological consequences in the Colorado River Delta and the Gulf of California. are there any parks at the former location of the river mentioned earlier? Yes, the southwestern United States contains many well-known national parks including Grand Canyon , Death Valley,  Great Sand Dunes ,  Arches, etc.
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Southwestern United States [SEP] Arrival of Europeans
The first European intrusion into the region came from the south. In 1539, a Jesuit Franciscan named Marcos de Niza led an expedition from Mexico City which passed through eastern Arizona. The following year Francisco Vázquez de Coronado, based on reports from survivors of the Narváez expedition (1528–36) who had crossed eastern Texas on their way to Mexico City, led an expedition to discover the Seven Golden Cities of Cíbola. The 1582-3 expedition of Antonio de Espejo explored New Mexico and eastern Arizona; and this led to Juan de Oñate's establishment of the Spanish province of Santa Fe de Nuevo México in 1598, with a capital founded near Ohkay Oweenge Pueblo, which he called San Juan de los Caballeros.