Best Stopover Between Phoenix and Boise

St. George, Utah—roughly halfway—is an excellent stop with attractions:

• Snow Canyon State Park (red rock canyons, desert views)
• Zion National Park (short drive, iconic cliffs, slot canyons, waterfalls)
• Tuacahn Amphitheater (outdoor Broadway shows)
• Sand Hollow State Park (swimming, boating, fishing, hiking)
• Dixie State University (cultural events)

Plenty of dining, lodging, and shopping. Other notable stops: Flagstaff (AZ), Las Vegas (NV), Reno (NV), Twin Falls (ID).