We go to the South Fork area (south central CO) near Wolf Creek Pass every summer. Beautiful area with lots of RV parks and campgrounds. Easy day trips to Pagosa Springs (hot springs), Creede (old mining town/ruins), Sand Dunes, Cumbres & Toltec steam railroad, etc.
It can still be pretty cool in May and early June since the elevation is about 8,500'.
Sand Dunes are interesting, especially when Medano Creek is still flowing with its shallow pulsing waves across the lower dunes. (it typically dries up toward the end of June).
And I also recommend the Cumbres & Toltec steam railroad if that interest you. An all day affair. I recommend taking the train from Antonito to Chama, and the bus back. Starts off in an arid climate, climbs slowing into the high mountains, stops for lunch midway, and then descends into Chama. The bus back lets you relax for a bit.
From I-25 you can take US 160 at Walsenburg across southern CO to South Fork and beyond. Or you can take US 50 from I-25 at Pueblo over to Poncha Springs (taking in Royal Gorge on the way), and then US 285 down to US 160.
A relatively short trip from Alamosa down to Santa Fe if you want to visit that area.
