Lace up for an unparalleled Earth Day celebration at the TMC Earth Day 5K at Biosphere 2 on April 18, 2026, in Oracle, AZ. This unique 5K run/walk, hosted entirely on the scientific grounds of the world-famous Biosphere 2, offers participants a rolling 3.1-mile course with stunning desert and mountain views, nestled against the majestic Catalina Mountains. The race begins and ends on the beautiful Great Lawn and features a mixed-terrain route, primarily pavement with a brief dirt section, and an elevation of approximately 3820 feet at the start. Expect a challenging yet rewarding experience, including an initial steep downhill, a climb past the Biosphere 2 complex, and a final uphill push to the finish line. Strollers are welcome, though runners should be mindful of the hilly sections.

Beyond the scenic challenge, the TMC Earth Day 5K stands out for its immersive experience and commitment to environmental stewardship. Produced by Run Tucson in partnership with the University of Arizona and Biosphere 2, this annual event has garnered positive feedback from runners, often described as "fabulous" and a "great time" with a "scenic" course. All participants receive free entry to an informative post-race tour of Biosphere 2, providing an exclusive look into its diverse ecosystems, including wetlands, rainforests, and even an ocean biome. Typical race day conditions in April present pleasant weather, with highs around 80F and lows around 53F, and a minimal 1% chance of precipitation, making for ideal running weather as you celebrate Earth Day and contribute to the Biosphere 2's Ocean Reef research project.

The event ensures a festive atmosphere with live music, an aid station at the 1.4-mile mark, post-race snacks and hydration, and various food trucks offering delicious fare for purchase. With a Free Kids Dash and children's activities, it’s a perfect outing for the whole family, offering not just a race but a day of exploration and celebration. All finishers receive a souvenir shirt and a timed result with a finisher's video. Plan to arrive early for packet pickup at the Biosphere 2 parking lot; carpooling is encouraged.