TMC Earth Day 5K at Biosphere 2 – Oracle, AZ 2026

March 31 Update: Here is the first pre-race email to all participants with race weekend details: Looking for a way to celebrate Earth Day? Join us at Biosphere 2 for a 5k run and walk, entirely on the grounds of the famed facility. Whether you're a seasoned athlete or just looking for a fun way to get some exercise, you're sure to enjoy yourself at the world-famous Biosphere 2. Clear your schedule and join us at the April 18th TMC Earth Day 5k, where you can walk or run the hidden Biosphere 2 backroads, nestled at the base of the majestic Catalina Mountains, north of Tucson. The rolling 3.1 mile course is perfect for racing and walking, with gorgeous desert and mountain views and a start and finish on the beautiful Great Lawn. After the 5k, you can relax, listen to music, snag some food, and enjoy other fun activities, so make sure to stick around to socialize and have some fun. Pricing: $40 for the $5k includes race entry, souvenir shirt, free Biosphere 2 entry (special price of $10 f