This is an exploratory style run that is the sister drainage to the north of Canyon Creek but you'll need to figure out a few things on your own. For one, the shuttle roads are complicated and you'll have to deal with gate closures that may preclude you from taking what appears to be the most efficient route on the map. There are some big V+ drops that are often portaged so proceed carefully.
Check out the
Middle and Lower Siouxon Creek trip report and the
Upper Siouxon Creek trip report on
Jason Rackley's site. He recommends hiking into the access for the upper and middle sections above Siouxon Falls. Below the falls, the creek is 90% class II-III, with multiple portages. There is a bridge just above the confluence with the North Fork that can be used as a take out, beyond that it's fun class III followed by a four mile paddle out on the reservoir.