Pacific edge
The Pacific coast is a sport-tourer’s road when you stay on the highway: damp pavement, tightening curves, wind that changes at every headland, and fog that can sit on the lane until late morning. A used Concours 14 is in its element here. So are an FJR1300 and an ST1300. The fairing matters. The shaft means you are not oiling a chain in a salt mist. Hard cases hold a rain layer you will actually use.
Leave the highway for the forest roads a ridge inland and the job changes. That is older R1200GS or CRF1000L country, or a Tiger 800 if the connector is narrow. A Concours will survive a short gravel surprise. It should not be the plan. An XRV750 can do the dirt and will feel out of its era on a long, windy coastal slab.
Season, without a calendar pinned to the wall: winter storms close the fun even when the road is technically open. Summer can be fog on the California stretches and clearer further north, or the reverse by afternoon. Spring and fall are when a lot of riders go, because the light is good and the campgrounds are less full. Tires should be for wet pavement if the forecast is a shrug.