The Doxie Derby is the dachshund race that takes place every year during Picnic Day. It's incredibly well-attended, and people get very excited (as do the dogs). There are both regular and mini-dachshund categories, and the races are hilarious to watch as some dogs tend to wander about instead of racing. Some doxie owners train their dogs to compete but others merely enter for fun.
The races take place in the Pavilion at ARC, formerly known as the Rec Hall, and a recent innovation was the "doxiecam," which was attached to the head of one of the little dachshunds and played footage on the scoreboard screen.
If you're planning on attending the Doxie Derby, it's highly recommended you get there early, both because it gets rather crowded later on and because some think the races closer to the beginning are much more fun, with dogs running all over the place, and owners doing everything possible to get them to go where they're supposed to.
For more information about the Doxie Derby and how to enter your dog, see http://ucdavisdoxiederby2015.weebly.com put up by UCD's School of Veterinary Medicine.