TMC Earth Day 5K

Event overview

The TMC Earth Day 5K at Biosphere 2 is a running and walking event held in April 2026 at Biosphere 2 in Oracle, Arizona (32540 S. Biosphere Road). The main course is a 3.1 mile route entirely on the Biosphere 2 grounds, with a start and finish area on the Great Lawn. The route runs at the base of the Catalina Mountains and includes rolling terrain.

Distances

• 5k (3.1 miles)
• Children's 5k (open to ages 1 - 14)

Features and logistics

The event includes a timed 5k with finisher video, age-group and overall awards, and free entry to Biosphere 2 for registrants. The first 600 registered participants receive a souvenir shirt (sizes limited). The course surface is mostly pavement with a brief dirt section and has hilly segments; strollers are allowed and pets are not permitted. Post-race offerings noted by the organizer include food trucks, snacks and drinks, a Kids Dash and children’s activities, and opportunities to tour Biosphere 2. Packet pickup is available at The Running Shop prior to race day. The event raises funds for the Biosphere 2 Ocean Reef research project. Visit the organization's website for the most recent information.

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