Guernsey SP WY

Guernsey State Park is about 3 hrs drive from Longmont, CO. So a good days' distance for us to go directly north.

Their RV campstites aren't exactly level, and they're not paved, so the muddy-gravel mixture makes using leveling ramps problematic.
A very active railroad runs through the middle of the park. We heard (and saw) trains running through every 30-60 mins, about 100 yards from the SW campgrounds. The trains run 24 hrs /day, so you do get used to the low rumble noise by nightfall (thankfully there were never any train whistles that we heard).

Be aware that many roads in the park are gravel, so weather may affect road conditions more than usual. While the main Visitor Center / CCC Museum is very nice with an excellent view, it can be a tricky uphill gravel climb in an RV.
Guernsey SP has perpetual algae blooms so they drain the reservoir once /yr. If boating or swimming, you'll likely not want to visit during the draining month.

We did see numerous small flocks of turkey, various other birds, and a few deer.
On the drive up we saw some pronghorn deer, and of course the ranch of bison.

Other than watersports and some nice views of the Guernsey Reservoir, the main draw of this location for us was the central location to some neat history.

Very close by are historical sites for the Oregon Trail.
Torrington, WY also has a neat museum that may be convenient to visit.

A good hour north, the small town of Lusk, WY has an amazing Stagecoach Museum. Unfortunately, there's not much else to Lusk, so may not be worth the drive for everyone.