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Two and a half days you've got more than twice the amount of time you need to get from Portland to Calistoga, and so you will indeed have time to wander a bit. Now there are certainly a ton of state parks along the Oregon coast and you could use up a lot of your time seeing a few of those and driving the summer-traffic-clogged Pacific Coast Highway. So you might want to consider another choice - inland for the first part of this trip, heading up the Columbia River Gorge to The Dalles then south on US-197 through White River Falls State Park to Axford, a possible side trip to the Clarno section of John Day Fossil Beds National Monument, and US-97 south. You could then use OR-138 west to enter Crater Lake National Park from the north and exit on OR-62 southwest to Medford, I-5 north to US-199 south and the PCH at Crescent City setting you up for visiting Redwoods national and state parks around Orick. You'v4e then got a chance to see some coast by taking CA-1 a bit farther south through Westport and Mendocino with CA-128 providing your best route inland to Calistoga.

On such a route, overnight stops might be in or near Crater Lake NP and then around Leggett CA after seeing the Redwoods, or a little farther south depending on how much time you wanted to spend on the coast the next day. The downside of such a route is that it will take just under two full eight hour driving days. All stops - food/fuel/sightseeing - are extra. Still, that would leave two to four hours each day for hiking.

AZBuck