Out of state visitors must still purchase an OHV decal for ATV use. However, you can avoid purchasing a decal if you meet ALL of these exemptions: You are not a resident of Arizona, you own the vehicle, you display a current OHV decal or registration from your home state, and your ATV is not in Arizona for more than 30 consecutive days.
Check out these San Tan Valley, AZ ATV/OHV resources:
