September ain't so bad, usually a few drizzly days but rarely any heavy storms or cold temps (although it will undoubtedly be cooler than SoCal). Bring a light rain repellent jacket, maybe throw some fenders on, but don't worry too much. As for the HCRH, the ride out to Cascade Locks is pretty awesome, especially the new car free sections. Thunder Island Brewery is just a few blocks past the end of the trail; OK food, good beer, great people and location. Heading East out Wyeth Road is fun, and there is a campground at the end of the road, but you are then unceremoniously dumped onto I84, which sucks terribly. Personally, I didn't feel it was worth it to continue on past Cascade Locks (despite an excellent dinner/beer at Pfriem in Hood River). Lot's more fun options heading out to the coast or South around Mt. Hood. Nestucca River Rd is a great way to get to the coast with campgrounds just after the peak of the coastal range.