2027 Registration Open

Celebrate Earth Day with purpose and adventure at the TMC Earth Day 5K! Set against the majestic backdrop of the Santa Catalina Mountains, this unique event invites runners and walkers of all ages to explore the hidden backroads of the world-famous Biosphere 2.

Whether you are pushing for a personal record or enjoying a scenic family walk, our rolling 3.1-mile course offers stunning desert vistas, culminating in an exciting finish on the iconic Great Lawn, set against the iconic architecture of the Biosphere 2.  

Free souvenir shirt for all registrants with a special add-on commemorative medal for sale, too!

Event Highlights & Registration Details

Event Date: Saturday, April 18th

Scenic 3.1-Mile Course: A hilly route through private Biosphere 2 grounds with panoramic mountain views.

Adult Registration ($40): Includes official 5K entry, a timed bib with a personalized finisher video, a souvenir shirt (first 750 registrants), post-race snacks, and free adult admission to Biosphere 2.

Youth Registration ($10): Special pricing for children ages 14 and under includes 5K entry and Biosphere 2 access (shirt not included).

Spectator & Guest Admission Discount: Race morning spectators are free. Non-running guests can purchase discounted Biosphere 2 admission for just $10 (when purchased before 8:30 AM); children under 12 receive free entry.

Exclusive Biosphere 2 Experience

Your race entry unlocks self-guided access to the 3.14-acre living laboratory. Go behind the scenes to discover cutting-edge environmental research—including the Landscape Evolution Observatory—and journey through diverse indoor ecosystems: rainforests, wetlands, savanna grasslands, fog deserts, and a living ocean.

Post-Race Celebration & Cause

• Morning Festival: Stay after crossing the finish line for live music, kids' activities, local food trucks, and post-race refreshments.

• Awards & Recognition: Overall and age-group awards generously provided by The Running Shop.

Run for the Reefs: Proceeds directly support the Ocean Reef Research Project, advancing critical solutions for growing resilient ocean reefs in a changing climate. See details and donate here. 

Turn your Earth Day into an unforgettable outdoor experience—register today to run, explore, and support groundbreaking planetary science!

What you get:

• Souvenir shirt to first 750 registrants

• Timed 5k with finisher's video

• Age group and overall awards courtesy of The Running Shop

• Free entry to the world-famous Biosphere 2

• Snacks and drinks

• Food trucks with yummy post-race food for purchase

• Children's activities

Schedule 

Thursday, April 16
4:00 - 6:00 pm Packet pickup and in-person registration at The Running Shop, 3055 North Campbell, Tucson
T-shirts to the first 750 registered, sizing and style on a first-come, first-served basis.
Yes: you can pick up the number/shirt of other people
Yes: you can shop for cool goodies at The Running Shop. 
Yes: It may be crowded, so please be nice to everyone
Yes: Be sure to take pins and pin your number on the front of your racing shirt.

 
Saturday, April 18 at Biosphere 2, 32540 S Biosphere Rd, Oracle, AZ 85739 
Please consider carpooling. Please park in the main parking lot at the Biosphere 2.  Please follow the directions of the Biosphere 2 staff on hand.

7:15-8:15 am Race day registration and packet pick up in the parking lot by the front entrance at the Biosphere 2.  Pick up your race shirt and colorful race bib number.
8:30 am Start time for TMC Earth Day 5k Run/Walk
8:30 or so: Food trucks, with snacks and drinks available for purchase
9:45 am Free Kids Dash on the Great Lawn
10:00 am Awards, courtesy of the Running Shop. Remaining shirts available to late registrants, first-come, first-served.
10:15 Event wrap-up
Tour the Biosphere 2: All registrants can visit Biosphere2 on their own -- no need for a formal tour! All non-running guests can purchase Biosphere 2 admission for the discounted rate of $10 (before 8:30 am) and all children under 12 are free.
 
Post-race: If you can't make the race weekend activities, please note that any remaining shirts will be brought to the Running Shop and available for pickup between April 21 - May 15. To get the size you want, pick up your shirt in advance.

Nice words from 2024 runner Dale: It’s important to me to thank the people who help make Tucson the awesome community it is! Saturday’s Earth Day was fabulous! I’ve been fortunate to attend all the races you’ve had out there! Just the view and space is incredible and what a gift to be able to “struggle” up the hills while taking it all in!   Thank you so much for all you and your staff/team do. 

Nice words from 2024 runner Louise: Wow!! Are you guys efficient or what?  Thanks so much for the quick turnaround with results and, again, for organizing and running a great event.  The water stop was especially appreciated on a hot day. (And even if we were running short of time, the announcer was funny and added an enjoyable element to announcing the winners.)

Bring the Kids!  Special $10 price for children 14-and-under in the 5k: includes race number, timing, and entry to Biosphere 2, but no t-shirt.

Running strollers are welcome, but be mindful of the steep hills and be sure to have the leash attached!

After the 5k, the little ones can enjoy the  free Kid's Dash & Kid's Zone activities.

Do Good! This event raises funds for the world-renowned Biosphere 2's Ocean Reef Lab. 

Terrain: mostly pavement, with a brief dirt section

Difficulty: hilly in sections

Weather: 50's - 70's

Differently Abled: Yes, be mindful of hills and dirt road

Pets Allowed: No

Want Training Advice? Contact RRCA-certified running coach Tia Accetta at tia@runtucson.net. 

This event is a partnership between Run Tucson & the Biosphere 2, the University of Arizona 

Questions? Contact Race Director Randy Accetta at randy@runtucson.net.