So, not high alpine stuff?
Lost Creek Wilderness is close to both Colorado Springs and Denver. It's one of my two "backyard" spots from Colorado Springs. If you're not going very far west it's probably your best bet. Lot's of various loops to string together, there. Not the usual "Rocky Mountain Experience" in that it is forested and not remotely alpine. Dondo and Pmags, both of whom are far better photographers than I, have some outstanding photos in trip reports on their blogs:
http://www.pmags.com/?s=lost+creek&submit=Search
https://dondo1.wordpress.com/2011/07/07/lost-creek-box-canyon/
It helps that even if you decide to bushwhack off of the well-established trails you still CANNOT get lost in Lost Creek. You can get a might confused for a bit, but not lost. All you have to do is go up a nearby hill and look around.
Here's a trip report of mine from a different region- the South San Juans:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=67107
That would seem to meet your criteria- mostly forested, clear trails. It looks a lot like your pics. But is probably a bit off your route. You'd have to loop way south through Alamosa and the San Luis Valley on Rt.160 to get there.
I keep thinking of great loops that size- like in Indian Peaks- but they're far more rugged than I think you want.
If you go out through Aspen (and the drive through Independence Pass is spectacular) then the Maroon Bells Four Pass Loop is probably considered THE classic Colorado loop hike of that size. It's up high, though- it's more alpine than your pics- but well trod and easy to follow. That time of year it tends to see a lot of traffic, though.
Also lots of potential loops in Flat Tops Wilderness near Glenwood Springs (bonus to have the Glenwood Hot Springs to recover in). And it also looks like your pics, not high alpine per se, though there are of course some trails on a high exposed plateau. But that may be a bit out of your way if you're just hitting Kremmling. Dondo, again:
https://dondo1.wordpress.com/2013/08/17/flat-tops-wilderness/
Bear in mind that he has pics of some extreme stuff- like the Devil's Causeway- but it isn't all like that, especially if you stay on the west side. The trails may not quite be as well-defined as you want, though.
If you are heading west a bit are you going through Buena Vista and Leadville? I'm sure you could find a loop in Collegiate Peaks Wilderness (another bonus for nearby Princeton Hot Springs). I'd need to check my maps when I get home to name anything, though.
I'm a fan of the Sangre de Cristo Mountains and Great Sand Dunes National Park, which is my other "backyard" spot from Colorado Springs. Not many nice loops there, though- certainly not on well-established trails. Most of such loops are on the east side and involve part of the Rainbow Trail, which is open to ATV traffic. The Venable/Comanche Loop is possible and doesn't involve the ATVS but is probably just an over-nighter. I've never done it, though, so I cannot testify to trail conditions. It goes over the ridge and back, including part of North Fork Crestone Trail. (Hmm, maybe I'll scout that for you if the snow melts out soon…) If you aren't hard on loops there are lots of spectacular out-and-back hikes in the Sangres comfortably close to Colorado Springs. And one shuttle I've wanted to try is having a drop off to hike over Music Pass, down Sand Creek, and out through Great Sand Dunes. It's probably 3 days.
If you're in Colorado Springs and claim to be a trail runner… an ambitious dayhike is to the top of Pikes Peak and back via the Barr Trail. 7800 feet of elevation gain in 13 miles, woop! (One-way.) Most folks have to hit the trailhead pretty early to pull it off, though. And to get decent parking. As in 04:00. I got there at 05:00 once, wasted time finding parking, and didn't quite have time to summit. But I'm old and slow. Supposedly someday there will be a Ring-the-Peak Trail around Pikes Peak- sort of a mini-Wonderland Trail- but it does not yet exist except in disjointed and unconnected fragments. There's a way to do it, but it involves an awful lot of road-walking.
Hey, I wonder if there is a way to summit Pikes Peak on the Barr Trail, go down Crags Trail on the back side, and connect it to the northern bit of Ring-the-Peak that's finished to go back to Manitou Springs. Hmm. Does Crags connect? I'll look into it when I get home to my maps.
While I was looking at Dondo links I found another report that piqued my interest, but I don't know much about it:
https://dondo1.wordpress.com/2013/07/14/snowmass-and-willow-lakes-loop/