Your description 
Another view
Is there anything in them besides gravel?
Something Cajun? 😉 Mon boxes on some bizarre curve!
Are those points under the canopy of a large live oak whose roots are partially covered by pavement? It looks as if their function is to improve soil aeration and to allow some water penetration. I think I'd call them "dry wells" until something better came along.
Series of drains to prevent ponding?
I can't tell whether this is in a roadway or in a pedestrian area.
If the latter, I suppose somebody once put in steel pipe posts to make a barrier and later they were cut off to open up access.
That's what I was thinking.
Concrete core samples that weren't filled after testing?
Maybe holes where bollards used to be? Possibly for a bicycle parking area? Is there a fire hydrant nearby?
Kent got it and I knew that he would.
A series of pvc with gravel placed along the drip edge of a 34" diameter Live Oak in a recently built parking lot.
Live Oaks are very protected in this locale nowadays.
Ancient trees can be designated as historical and prevent construction. Recently an exclusive girls prep school was denied a permit to build because it would remove some "historic oaks". Pretty crazy.
Here is the tree in Slidell
I guess that you noticed some acorns and the shadows.
Earlier in the day, the shadow aligned with the holes which was pretty neat.
Way cool!
Maybe an appropriate place for hydromedia ?
Cheers,
Derek