Popular distances
Triathlon
Popular places
Events
Parkruns
Organisers
Charities
Guides
Articles
Nothing matches “” yet — try a place, distance or event name.
Duathlons found in California in December
There are no 'Duathlons in California in December 2026' in the calendar at the moment, but why not take a look at all upcoming Duathlons or see what other exciting challenges are available for you in 2026.
Organisers add new races every week. We'll email you as soon as one matches.
Free, and you can turn it off anytime.
Cookie settings
Cookies are small text files a website stores on your device. Choose which ones we can use below. You can change your mind at any time.
These cookies keep the site working: signing you in, remembering your basket and checkout, protecting forms, and keeping payments secure. They can't be switched off.
These remember choices you make, like your approximate location when you share it or the place you choose to see events near, events you've opened, or that you've dismissed the regional site prompt. They're only set when you use the feature.
These track your browsing across websites so we and our partners can show you more relevant adverts. We don't set any at the moment. If we add them, they will only be set if you allow them here.
See every cookie we use, and how long it lasts, on our cookie information page.
Win a $250 nike.com gift card!
Every month, one lucky subscriber wins a $250 digital gift card to spend at nike.com. Sign up for our emails and you're in.
All done, you're in!
Thanks for signing up — watch your inbox for news, offers, and your chance to win.
