From Hwy 30, cross the bridge to Sauvie Island and head north passed the store. Turn right onto NW Reeder Rd and take it all the way to the end. Just before the beaches, the road turns to dirt. There are big sections of washboarding.
A parking permit is required on the island: https://sauvieisland.org/visitor-information/park-permits/
Length: 6.5 miles round trip
Elevation Gain: 42 feet
Type: Out & Back
Duration: 2 hours
This is an easy hike. I'm surprised that AllTrails shows any elevation change. There is one fallen tree that you have to go around and a couple others that you can walk through single file. Otherwise, the trail is wide and was apparently used as an access road to the lighthouse in the past.
You cannot climb on or inside the lighthouse. It's not the kind with a Fresnel lens, but cool landmark to see.
"Warrior Rock Light is a lighthouse on Sauvie Island in the U.S. state of Oregon, which helps guide river traffic on the Columbia River around the Portland, Oregon area. It once contained the Pacific Northwest's oldest fog bell. It is Oregon's smallest lighthouse, and the only lighthouse, or one of only two lighthouses, still operating in Oregon which are not on the Pacific Ocean, depending on whether the Umpqua River Lighthouse is considered to be on the coast or on the Umpqua River."
Some more views from the point:
Difficult to see, Mt St Helens is peeking over the horizon, right of center (photo below). She is pretty barren of snow at the moment.