All our local dog parks are separated for small dogs (under 25 lbs) and big dogs. But if your yorkie is 3 lbs and is up against a 25 lbs dog, that is still a big difference! Also, one park in Irvine, several dogs got sick after a meetup, so yes it is possible.
http://www.yorkietalk.com/forums/cal...-dog-park.html
Also, please keep in mind that Britster's dog park is like the 3rd best in the country, so she is very lucky, and I am super jealous. Most dog parks are not that nice, and most people that frequent them are not as responsible as in her area. So be careful, be UTD on shots. We do the same thing as Timba212, go to a regular park and throw the ball around. Uni doesn't play well with other dogs anyway. Well other than Kaji of course!