TMC Earth Day 5k at Biosphere 2

TMC Earth Day 5k at the Biosphere 2, April 19, 2025

Looking ahead to 2025: Registration now open, with $25 low price through June 30, 2025.  

Finishing up 2024: Click here for the first race report and see our timer’s page for race results: www.roadrunnerracetiming. All age group and overall awards are at The Running Shop, 3055 North Campbell Avenue.

Looking for a fun way to explore one of the most popular tourist destinations in Arizona? Celebrate Earth Day and join Run Tucson on Saturday morning, April 19, 2025 for the TMC Earth Day 5k Run/Walk entirely on the grounds of the world-famous Biosphere 2.  Run the Desert . . . then visit a rain forest, view an ocean reef, and wander through savanna grass lands . . . all in one day!

Registration and Updated Race Info Here:

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, 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 live music, snag some food, and enjoy other fun activities, so make sure to stick around to socialize and have some fun. All registrants receive free entry to the Biosphere 2 informative tour of the renowned research facility, with an exclusive peek into the inner workings of the Biosphere 2, a wild world of wetlands, rainforests, grasslands, fog deserts, and the big blue ocean. It’s like a backstage pass to nature’s superstar habitats!
The TMC Earth Day 5k is raising funds for the Ocean Reef research project, learning how to grow ocean reefs in a changing climate.  See details and donate here. 
What you get:
  • Souvenir shirt
  • 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
  • Live music and other activities

Start Time: 8:30 am 5k Walk/Run, followed by Free Kids Dash.

Produced by Run Tucson in partnership with the University of Arizona and Biosphere 2

The rolling 3.1 mile course offers gorgeous desert and mountain views, with start and finish on the Biosphere 2 Lawn.  Don’t miss this chance to visit the earth’s entire ecosystem under one roof while celebrating Earth Day.

 Click here for the video our wonderful race photographer Damion Alexander put together.

Calendar listing at and at Visit Tucson. =

2024: Awards available at Running Shop through October 1, 2024
2025: Packet Pickup and Registration Dates
Friday, April 18
at The Running Shop, 3055 North Campbell, Tucson
4:00 – 6:00 pm Packet pickup and in-person registration.
Saturday, April 19
at Biosphere 2, 32540 S Biosphere Rd, Oracle, AZ 85739

7:15-8:15 am: Race day registration and packet pick up at front entrance to Biosphere 2
8:30: Start time for TMC Earth Day 5k Run/Walk
9:30: Free Kids Dash
9:45 or so: Awards, courtesy of the Running Shop. Remaining medals and shirts given to late participants

10:00 Event wrap-up

Ongoing: All registrants can visit Biosphere 2 on their own — no need for a formal tour!
All non-running guests can purchase Biosphere 2 admission for the discounted rate of $11 (before 8:30 am) and all children under 12 are free.

Distance: 5k Run and 5k Walk. Click here for all the route details and more.

Bring the Kids! Strollers are allowed at this child-friendly event, with a free Kid’s Dash & Kid’s Zone

Do Good! This inaugural 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

Runner Quote: Amazing course.  Great setting and wonderful cause.  Thanks again.

Weather: 50’s – 70’s

Chair Athletes: Chair athletes may find this a doable but challenging course, with a couple of steep hills and the dirt road.

Pets Allowed: No, pets are not allowed on the Biosphere 2 grounds.

Want Training Advice? Contact RRCA-certified running coach Tia Accetta at  



Terrain: The race starts and ends on grass, but it’s mostly pavement, with a brief dirt section … and, well, it’s hilly in some sections…
The Start: The event starts on the grass of the Great Lawn, crosses some gravel, then drops down a steep hill before heading up another steep hill that passes the Biosphere 2 complex. There are a few speedbumps on this opening hill, so please keep an eye out for varied terrain.
Mile One: After the first half-mile or so, you’ll continue heading north on a mostly flat section, before taking a sharp right turn and plunging downhill. Off to your left will be the Catalinas as you head downhill, then you’ll begin a gentle climb back up to the beautiful dirt road section, with the mountains to your left and the Biosphere 2 to your right.
Mile Two: The second mile will be a bit twisty as you go past the historic ranch house, then swing downhill past the stables and onto the flat-ish out-and-back. There will be about a 1/3 of a mile of gentle downhill to the turnaround, then you’ll come back heading towards the Biosphere 2.
Mile Three to the Finish: The final stretch will head back up the hill to the finish line in the middle of the Great Lawn.
Chair Athletes: Chair athletes may find this a doable but challenging course, with a couple of steep hills and the dirt road.
Strollers: Strollers are allowed in the race, but please be mindful of the hills and ensure that you are tied to the stroller you’re pushing. Please remember sun protection.
Measurements: The route is garmin- and map-my-run correct but not a USATF certified course. The mapmyrun online map is here.
Headphones: We request that you do not wear headphones while participating in the event. Enjoy the camaraderies of your fellow athletes, enjoy the scenery, and keep an ear open for rattlesnakes, javelinas, and other participants.
Wildlife: This event takes place in a rural environment adjacent to wilderness, so you may encounter any number of wildlife, including but not limited to rattlesnakes and other snakes, javelina, cattle, deer, wild turkeys, bobcats, and more. Please do not try to touch the wildlife. Please do not wear headphones.
Heat and Altitude: The race starts at approximately 3820 feet, so be mindful that you’re at a bit of elevation. It looks like race morning may be about 50 degrees at the start, climbing to the mid-70’s. Stay hydrated, wear sunscreen and a hat.

Click here for links to past year race results from our good friends at Roadrunner Race Timing.

Click here for photos from 2024, courtesy of John Harris.

The TMC Earth Day 5k is a 30 minute drive from Tucson and a bit more than an hour from Phoenix.

Directions to Biosphere 2 From Central Tucson
From central Tucson, go north to River Road and turn left (heading west)
Continue on River Road and turn right on Oracle Road/AZ Highway 77
Drive north approximately 24 miles on Oracle Road/AZ Highway 77
Turn right on to Biosphere 2 Road at Mile Post 96.5

From Phoenix Sky Harbor International Airport
After leaving the airport, follow the signs to I-10 E
Take I-10 E toward Tucson, to Exit 185 and exit the interstate
Turn left onto Highway 387 and continue past Coolidge until Highway 387 intersects with AZ Highway 79 near Florence
Turn right on to Highway 79 and follow this until Oracle Junction where you turn left onto AZ Highway 77
Drive north approximately 6 miles on AZ Highway 77
Turn right on to Biosphere 2 Road at Mile Post 96.5

Please carpool. There will be parking in the Biosphere 2 parking lot, but it would help if participants carpooled to share the drive.