Registration is open.
Likely to sell out. 686 finished the 5K in 2026, and this year's cap is 700.
We earn a small commission when you register through this link, at no cost to you. Details
Official race websiteAdd to calendar: Apple or Outlook · Google
| Event | Distance | When | Entry fee | Cap |
|---|---|---|---|---|
| Children's Discount | 5K | Apr 17, 20278:30 AM | $12 | 100 |
| TMC Earth Day 5k Run/Walk | 5K | Apr 17, 20278:30 AM | $40$45 after Apr 1, 2027 | 700 |
Entry fees exclude processing fees. Prices and dates come from the race's registration page and refresh nightly.
The 5K fee goes up to $45 on Apr 1, 2027.
Online registration closes Apr 17, 2027, unless the race fills first.
At $12, entry is about 66 percent below a typical 5K in Arizona, which costs $35 right now.
A typical finisher at a 5K in Arizona runs 36:32, about 11:46 a mile, based on 82 races with published results. Women typically finish in 39:22 and men in 31:47.
Sunrise on race morning is at about 5:52 AM, and the Children's Discount starts at 8:30 AM. The start sits about 4,100 feet above sea level, high enough that most runners from lower ground run noticeably slower.
Fees exclude processing fees. Comparisons use current entry fees and published results from races nearby.
32540 S. Biosphere Road, Oracle, AZ 85623
The pin marks the address the race lists, which is usually the start. The organizers have not shared a course map with us yet.
Aggregated from official results (Roadrunner Race Timing) for TMC Earth Day 5K at Biosphere 2. Individual finisher names are not stored here.
In 2026, the fastest tenth finished in 27:41 or better, the top quarter in 33:22, and half the field in 41:56; the last tenth came in after 1:03:13.
| Age | Women | Men |
|---|---|---|
| Under 20 | 29:38 | 26:32 |
| 20-29 | 24:41 | 20:59 |
| 30-39 | 25:30 | 22:10 |
| 40-49 | 26:54 | 25:38 |
| 50-59 | 31:29 | 24:33 |
| 60-69 | 31:04 | 30:40 |
| 70+ | 37:46 | 29:00 |
Groups with fewer than five finishers are left out. Awards vary by race; check the race's rules.
Where a finish time would have placed in 2026.
Up 12 percent since 2025.
All events combined, from official results.
From 2025 to 2026, the field went from 611 to 686 finishers, and the median time rose from 39:12 to 41:56.
| Year | Finishers | Median | Fastest tenth | Winner |
|---|---|---|---|---|
| 2026 | 686 (+12%) | 41:56 | under 27:41 | 19:30 |
| 2025 | 611 | 39:12 | under 27:06 | 17:31 |
From each year's official results for the 5K; virtual options are left out.
Slower than most Arizona 5Ks
The fastest quarter of the 2026 5K field finished under 33:22, against 30:59 in a typical Arizona 5K, so times here run 8 percent slower.
Compares the fastest quarter of each field, so walkers and first-timers do not skew it. It reflects the course and the field together: a flat course, cool weather, or a competitive crowd all make times faster.
Around April 17 the day usually runs from 54°F at dawn to 82°F in the afternoon, with measurable rain on about 0% of days. Cold snaps dip to 48°F and hot years reach 88°F.
Based on 75 days within a week of the date over the last 5 years, from historical weather for the start area. Not a forecast.
What the organizers of TMC Earth Day 5K at Biosphere 2 cover on their registration page, in brief.
Parking and travel
Address: 32540 S Biosphere Rd, Oracle, AZ 85739. You can park in the main visitor lot at the Biosphere 2. Please carpool. There will be parking in the Biosphere 2 parking lot, but it would help if participants carpooled to share the drive…
Parking and travel
Discounted hotel rooms at El Conquistador Hilton: $195 plus fees, available Friday, April 18 and Saturday, April 19. The famed El Conquistador Tucson is a Hilton Resort nestled against the western edge of Pusch Ridge, a mere 20 minute…
Shirt and medal
There are two options for kids: 1) after the race, we'll hold a free kids dash for children of all ages. They'll do a loop around the Great Lawn and we expect to have previous race medals to hand out to all kids. 2) we also offer a $10…
Rules and FAQ
Discounted visitor pricing, service animals welcome, no pets on site, and other visitor details. Discounted Visitor Pricing: All runners receive free entry to the Biosphere 2, while all all Earth Run spectators 13 years and older receive…
Organize this race? Add details or a correction
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