U.S congers+ Approves Time zones

The Earth rotates 15 degrees of longitude in an hour and, in the beginning, there was local time. Each community worked out its own time in relation to the sun. Standard time grew out of the need to create train schedules so that the trains could run "on time."standard time zones were established which covered approximately 15 degrees of longitude. Arizona is in the mountain time zone. But major population centers, Flagstaff, Phoenix and tucson, run down the center of the state which means that most of the population of Arizona is clustered towards the western edge of the mountain time zone. Communities on or near the colorado river are on the western edge of the mountain time zone.