SearchResearch Challenge (8/24/16): The mystery of the Hawaiian posts on the North Shore

It was a beautiful morning... 

... and I was running on a jungle path, getting my morning exercise while staying on the North Shore of Oahu.  

As I run or bicycle, I regularly discover small mysteries on the land.  In 2013 I wondered "Why is this tree here?," and in 2014 I wondered "What are these things that I see on the horizon?"  

So it should come as no surprise that I would find something even more mysterious while running in Hawai'i.  

I was jogging along the path in the middle of what seems to be just a regular forest--lots of trees, vines, well-developed understory--when I run past this: 

That seems odd and out of place.  Perhaps it's just a light pole that's been forgotten about.  

A little farther down the trail, I find this.  Another light pole?  Was there a road here that was built, but never fully completed?  

But then I started finding more and more of these poles--some just a few feet high.  The one shown below is around 6 feet (2 meters) tall.  The poles varying in height from 1 meter to 3 meters tall.  

These poles were standing by themselves, and not in any obvious pattern that I could see. They didn't seem to line up.

But then I found this collection.  

I'm not sure how many I found, but there are at least 30 poles like this of varying heights, all "lost" in the forest.  In Hawai'i, I might have thought this was the work of the menehune, the mysterious builders of Hawai'i that come and go out of human sight. But this was suspicious--someone was making something very mysterious.  

(And although I looked, there were no signs telling me what's going on here, or marks on the poles that would give us a clue.  They're just concrete poles of varying lengths.)  

By now, I'm curious, and looking all around.  I DID find a cache of them!  (See below.) 

Having once worked in a trucking company, I recognize this as a temporary cache of poles, all stacked atop a pair of poles laid sideways at right angles to the main pile.  This makes it easy for a forklift to come and pick one or two up off the pile and carry it to the next workplace.   (Yes, I know how to drive a forklift; the things you learn when working to pay for college...)  

No matter how many poles I found, whoever was doing the building clearly had to abandon the project in the middle.  

I'll save you the metadata EXIF extraction:  these photos were all taken within a 100 yard radius of 21.698574, -158.005291  

1.  What's the story with these mysterious poles in the jungle?  Why are they there? 

Fair warning:  I do NOT know the answer to this Challenge, so I'll be searching for the answer along with you.   

If you figure it out, be SURE to tell us what you did to determine the answer.  I've only spent a few minutes on this, but I suspect this will be a tough Challenge.  

Search on!