Welcome to the forum; and to my native state. I hope you like it here. You will find lots of places, with MUCH bigger trout...including Hagg. I've seen rainbows in the 6-7 pound range, hauled out of Hagg...many from the bank. And, there are some that are even larger! Hagg has also produced at least 2 state record smallmouth bass too.
Now, is the time to be fishing the Sandy and Clackamas for Springers and Summers. You can use the search engine on here, and learn a LOT about how to fish for those fish. I also encourage you, to buy a copy of "Complete Angler's Guide to Oregon", by John Shewey. This book is available in most local fishing departments, and sporting goods stores. You will learn a lot, and get up to speed quickly, by reading that book.
I am sure, that some folks will OFFer to help you out too. There are a lot of really great, and knowledgeable, peeps on here. Good luck. We look forward to your reports. And don't hesitate to keep asking questions.