Boat Ramps in Arizona

Arizona boating is almost entirely lake boating, and the lakes here are reservoirs carved out of desert canyon country. That setting is stunning but it also means water levels fluctuate considerably depending on snowpack and drought conditions, both of which have been serious concerns in the Southwest for years. Before you trailer out to Lake Powell or Lake Mead, check current water levels - ramp closures due to low water have been common and sometimes the only usable ramp at a given lake requires a much longer drive than you'd expect.
Lake Havasu is probably the most social boating destination in the state, attracting a heavy spring break and summer crowd. The ramps there are well-developed but the traffic is real. If you want the same warm water experience with a fraction of the people, Alamo Lake out in the western desert is worth considering for bass fishing.
Roosevelt Lake northeast of Phoenix is the largest reservoir entirely within Arizona and has good Corps of Engineers ramp infrastructure. Saguaro and Canyon lakes in the Salt River chain are smaller and have horsepower restrictions, so know those rules before you show up with a big outboard.
Year-round boating is legitimately possible in Arizona given the climate, but summer water temperatures on the lower elevation lakes get dangerously warm and the heat above the waterline is no joke. May and October are probably the sweet spots for comfortable, crowd-reduced boating across most of the state.