Moab, Utah to Mueller State Park ,Divide Co

CO 9 is a good road but has a fair amount of traffic, esp. through Breck.

Other options include turning off I-70 at Minturn and taking US 24 through Buena Vista. A little further but you avoid Vail Pass that way plus all the traffic in Summit County.

Of course you could take US 50 from Grand Junction to Poncha Springs, north on US 285 to almost Buena Vista then right on US 24. The biggest pass on that route is Monarch Pass.

Hiway 9 is a good road but there will be construction between Frisco and Breckenridge (9 miles or so). The climb out of breckenridge is a bit scary if you are not used to mountain driving but very doable. An alternative is to turn off at I70 at Minturn on US 24, thru' Leadville and on to the Mueller S.P. turn off.