Hmmm... That's odd. I see you live in CO.... My younger brother moved to CO about a year ago and from what he's told me, it's a lot more dog friendly than our home state of WI... He said you guys have "Small Dog Wind Warnings". I can't decide if he's joking or not... is that true?!
I pulled this link from the Colorado State Parks website. It's the 2006 State Parks Regulations. Under Animals/Pets on page 4 it says:
"To allow any dog or other pet on Parks and Outdoor Recreation Lands, unless the same shall be under control and on a leash not exceeding six (6) feet in length. This requirement for dogs or other pets to be on a six foot leash shall not apply when the animal is confined in a vehicle or vessel. Further, it shall be unlawful to allow a dog or other pet within any area used as a bathing or water-ski beach. Any person having a dog or other pet creating a nueisance or disturbance who fails to properly control a dog or other pet may be evicted from the park or reacreation area. This provision shall not apply to dogs while being used in hunting, field trials or while being trained on lands open to such use."
See:
http://parks.state.co.us/images/cont...gs20061871.pdf
Throughout the document it lists a few parks where dogs are not allowed at all or are only allowed in certain areas... Were you at one of these parks?
Based on this I would think your pup is allowed in (certain areas of certain) parks... Maybe try getting a hold of the parks division and see what they have to say about it. If they it's okay... Maybe print this out and show it to anyone (along with a copy of the email from someone working in the parks division, if you decide to contact them) that your dog is indeed allowed there!