Boyce Thompson Arboretum is the largest botanical garden in the Western USA and is a one hour drive from downtown Phoenix. It showcases a wide variety of plants from deserts around the world, particularly focusing on those native to the Southwest. It's one of the best places to see fall colors in southern Arizona and the colors peak starting in late November and can last into late December depending on the year. Make sure to explore the Main trail, the high trail, and the suspension bridge during your visit. The entry fee is $25 per person age 13 and up and is $10 for kids age 5-12. The arboretum offers some free admission days like on the first Tuesday of the month from October through May, but pre-registration is encouraged since the free tickets are limited.