Pretty much anywhere you want, except close to the hatcheries. Check your regs. On the Seymour it is fly only above Spur 5. If you don't know where that is check your regs and maps.
Be careful in the cap, many dangerous cliffs and slopes to contend with. Knowing how to roll cast will help.
You will find the Seymour easier to fish as it's more open and easier to wade at this time of year. Lots of small trout, and probably a lot of steel and coho smolt in there, so please be very careful with catch and release, only use barbless hooks so they are easy to release in the water without handling them.
Any small nymph or olive bugger will work. You will also catch fish on a dry fly if you have a floating line.
There is some nice water above and below twin bridges, but it is a good hike in (which is good because you will have the river to yourself).
Go explore, have fun and report back.