Congratulations on taking a trip with your son. He'll surely remember this for years.
Once you get west, you'll find lots of camping opportunities on NFS, NPS, and BLM lands. One of the best ways I've found to located campgrounds is using
this campground map. Just type in a town you'll be near and it will zoom to that area, showing both public and private CG's. Also, if you haven't discovered it yet,
this is a good place to find more detailed information on NFS CG's around the US.
Six weeks may seem like a lot, but you'll have to be quite selective in where you'll go. Of course there's the obvious choices like Yellowstone and the Oregon Coast, but there are other beautiful places that aren't necessarily in the NPS system. For instance here in Colorado, I'd steer you to either a few days in and around the Leadville/Buena Vista/Salida area or to the Durango/Silverton/Ouray area. In either place, you'll find amazing scenery, great hikes, and ghost towns to explore. The river rafting on the Arkansas might be something your son would really get a kick out of. Durango is more convenient to Canyon de Chelly and you can also visit Mesa Verde while you are there. The
Durango to Silverton Narrow Gauge Railroad is an unbelievable ride through breathtaking scenery on an 1880's vintage railroad. Not some short little trip, but 45 miles each way on a full day excursion.
The Grand Canyon is indeed Grand, but another option is to head from Colorado to Moab Utah. Visit Arches and Canyonlands NP's. While not as deep as the Grand Canyon, we prefer the views from Island in the Sky at Canyonlands. Arches is otherworldly. While you're too late for reservations at Arches, there are BLM CG's right along the Colorado River. Just don't arrive on a Friday and expect to find a spot. Once you leave there, you can head west via I-70 and US 50/US 6 through Nevada and approach Yosemite from the east via CA 120.
(I would say that unless you have some relatives to visit in Las Vegas, I'd skip there altogether. There's so much better ways to spend time with a 16 year old.)
Yosemite can be very tough to get a place to camp w/o reservations. You'll find places like the Grand Canyon, Yellowstone and Yosemite to be incredibly packed in June and July. Traffic in Yosemite Valley can slow to a crawl during the day.
As far as travelling the coast, rather than CA 1, I'd head straight for the Oregon Coast. The state parks there are amazing as is the scenery (cheaper and more abundant SP CG's than CA). Since you are tenting, you'll have a lot more options for campsites than those in an RV, and there are still some of those sites to be reserved. On the southern OR coast, we like Harris Beach SP. Close enough to CA to visit the redwoods without putting up with the high cost of CA SP's. North from there, we like Sunset Bay SP and Beachside SP to name a couple. Check out some of the brochures
here, both for individual parks and for the tide pool and lighthouse brochures. They will help guide you explorations as you drive the coast.
On your trip from the coast toward Yellowstone, I'd head inland and follow the Columbia River upstream from Portland. The Columbia River Gorge has a number of great waterfalls. Follow the old highway (US 30) rather than the interstate. There are a couple of SP's along the gorge (we stay in Ainsworth SP when in the area). Check out
this brochure to plan your day.
With a tent, you'll have more opportunities to find a first-come, first-served CG at Yellowstone. Do plan on several days at Yellowstone, as driving through the park isn't quick and each section of the park has it's own unique scenery to enjoy. The Upper and Lower Geyser Basins and the Grand Canyon of the Yellowstone are the places not to be missed.
In fact I'll give the advice I often give here. I find it's better to spend a little more time in fewer places rather than seeing very little of a lot of places. If you're used to visiting "old dead guy's houses" on your trips, you'll find on your trip out west a whole 'nother world of vacation experiences.
I've given you lots of info here. Hopefully I haven't overwhelmed you. Have fun.
Ken & Allison
2 Camping Cats (1 diabetic)
1996 4Runner, TRD Supercharger, Edelbrock headers
2007 Fleetwood Arcadia, Honda EU2000i
4 mountain bikes, 1 canoe, 4 tents, 8 sleeping bags, 2 backpacks
(You get the idea!)