So as this thread drifts along...
If you are traveling across the west and you do not need particularly to go to someplace in Colorado I suggest following I-80 through southern Wyoming to Utah, or the reverse. Navigation is easy, I-80 actually is about 6000' MSL most of the way but you wind between the clumps of peaks and there are airports at good intervals. Weather is almost the same as Colorado, which means mostly clear with the odd crappy day. You don't have to fight the Rockies as the road builders found the easy way. In fact, I-80 follows the same route across Wyoming as the original transcontinental railway. Which followed the wagon train route.
I flew an antique airplane from Boston to San Francisco and back and essentially followed I-80 from coast to coast. Made crossing the Continental Divide relatively easy. For a more northern route, I-90 works. I Follow Roads....
To Bill's point, you have to look hard at a sectional chart to understand how the mountain passes are configured. For example, Donner Pass from northern CA to Reno NV is 7000' high. On a cloudy day you might not be able to make it. Or another example is Hot Springs AR. If the ceiling is 2500' you can do pattern work around the airport all day but you aren't getting out of the valley to go anywhere else. In areas like these you have to know how get get more info from your chart than where the airports and VOR's are.
And Hal, I will guess that if the ceiling at Snoqualmie pass is 800' agl, but you know that the weather is stable and also good on the other side, that can still be a very long 15 minutes.... But the short and narrow ranges are a great way to learn about flying around rocks. You can go see but back out quick before Mother Nature closes the door behind you.
Fly safe,
Wes
N78041