Did "Aliens" stack these rocks like this?

When Vegas Bob was on his trip in Northern California visiting the "Redwood Trees" he came across these rocks stacked around the river.

I have seen these rocks stacked like this around many hiking trails I hike along marking certain areas so hikers can find their way back on the right trail.

Now these rocks stacked by this river bed and in the water along the "Van Duzen" river are just plain weird. VB didn't put these rocks there so he was wondering who did?

There wasn't a person within miles of this river ...

VAN DUZEN RIVER-NORTHERN CALIFORNIA