husker, I live CO, and that is a excellent area for riding. I have rode that area several times (none yet this year, have a Labor Day camping trip planned for that area) so I dont have any updates for this season. It is still possible some passes or trails are closed, they got a ton of snow up there this last winter, but by now most should be open. I would suggest finding a book called ATV Trails Guide Colorado, Taylor Park, Crested Butte, ( by Charles A Wells). Local atv shops, or even sometimes Barnes and Noble will have this book. It lists 30 trails, with maps and tips, and a lot of good info. You could probably also google Taylor Park area and get a lot of info.
My personal favorites are Alpine Tunnel, Tincup Pass to St Elmo ghost town, Hancock Pass, Cumberland Pass, Taylor Pass/Aspen Summer Road (takes you to town of Aspen, no riding in town, but you can stop at Sundeck Restaurant at top of Aspen Mtn). Hancock Pass is a good loop to add to Tincup Pass/St Elmo/Alpine Tunnel, but may not be good for the less experienced riders. Cumberland Pass is a good, easy trail, you can test out your Pioneer for speed on this trail, but be careful, you top out at over 12000 ft and there are some steep/curvy areas. There are many others also. All of these trails may have some steep/and/or rocky areas, but unless otherwise noted, aren't to difficult, your Pioneer will do great, but keep in mind if any of the others are not e.f.i., you will be above 9000 ft and up to 13000 ft on some trails. There are many difficult to extreme trails in the area also, so its best to find out any info you can before starting a trail. There are also several easy trails in and around Taylor River Road after Taylor Reservoir. I would suggest always start out with a full tank of gas, as some of these loops may be 70 miles or more, but you can get gas in a few places, like Taylor Park Trading Post, and I think Tincup also has gas.
If you haven't rode in Colorado before, I think you also need a Colorado OHV sticker for each atv, and they will stop you if they don't see a sticker. I have been stopped many times even with sticker displayed. You are supposed to have driver license to ride anything over 90 cc and be registered (OHV sticker). I believe it is $25 for each sticker. I think you can contact Colorado State Parks for more info, and how or where to get a sticker. But don't be intimidated, the rangers usually have great info on what trails are open in the area and the best ones to ride. Hope you have a fun safe trip, this area you will find some of the best high mountain riding (scenic, challenges, long rides) in the entire country.