Left Hand Canyon is 15 miles of fairly gentle climbing, followed by 1.5 miles of steeper stuff. Be sure to stop at the Utica Street Market in Ward and buy a Gatorade. We gotta keep that guy in business. I think cyclists must account for the bulk of his trade.
You can turn around there and make it a 33-mile ride. Or you can continue uphill 1/2 mile past the market, then turn right on the Peak-to-Peak highway (CO72). Descent from there to Lyons via CO72 (10 miles) and CO7 (15 miles). Then take US 66 and US 36 from Lyons back to the start (7.5 miles) for a 49-mile loop. The scenery on Peak-to-Peak is well worth the extra 16 miles, and it's not much more work because the descent is more gentle that way. The descent down CO7 is on a glass-smooth road with a gentle grade and gentle curves, such that for 15 miles you'll neither need to pedal nor brake.
If you want, you can take the marked turnoff (right turn) to Raymond on CR103 after 8 (of the 10) miles on the Peak-to-Peak. It's a shortcut (saves one mile and some rolling hills) over to CO7. This also gives you access to another general store in Raymond.