For those looking for mud, there's "Mud Loop"

[Jim]

TrailDamage has their "Mud Loop" set of trails. These are west of Fort Collins, up Hwy 14 / Poudre River.

Each trail is a through trail and all can be linked to make a long 40 mile route...

Sevenmile (Seven Mile) creek (12.1 miles)
http://www.traildamage.com/trails/index.php?id=92

Bald Mountain (13.1 miles)
http://www.traildamage.com/trails/index.php?id=274

Green Ridge (14.7 miles)
http://www.traildamage.com/trails/index.php?id=273

[alexb]

Is this doable in a day?

[Jim]

Hmmm... 40 miles at a trail speed (when moving) of perhaps 4 mph. One long day with no stopping or issues. I'd tend to think not. Or if tried, it could be a 6am trailhead start with a 10pm end. There is a fair bit of dispersed camping in the area if someone were to make it a two day event.

EDIT: IMO, when Sevenmile Creek is flowing, there's not a terrible amount of mud (I do recall a couple areas next to the creek that needed to be crossed that had mud). If Sevenmile is left out of the loop (and it easily could be), the other two would be for a reasonable, long 1-day event.