First, Thanks Clu for the O/P ;}
Thinking you are on the money ThoughtFox, as they can usually tell whether they are human bones. It seems they have garnered the forces for this discovery. If their basic thought was they were not animal this makes sense to me. Finding animal bones in areas like a creek bed must be quite common as we have a lot of cougar here that feed in our backyards.
The creek itself looks pretty normal for the area. Like getting down to it you can walk part way, winding through the vegetation and then maybe have to slide or go sideways down a couple of feet till it levels off again, etc.
These little creeks are where the fish spawn every year. They start out as little creeks up in the mountain areas and work their way down, joining each other and eventually dumping into the say Clackamas River which then dumps into the Willamette which dumps into the Columbia and then flows into the Pacific Ocean. Then every year, the Salmon leave the ocean and swim back upstream to the same place in that tiny creek where they were hatched and lay their eggs. It is amazing.
And if it is a dry creek bed that means water flows seasonally depending on the amount of rain or snow melt. So yes, in the Fall or Winter of the last year these bones could have washed down. We've had allot of flooding.
The condition of the bones made me think they were older than a year for some reason. IMO