SearchResearch Challenge (2/13/19): What's the story... of these ruined buildings?

Last week I was visiting Napa Valley... 

... and since it was a beautiful spring day, I went out for a bit of drone flying.  

I drove around for a bit, knowing full well that there are lots of rural roads that are dead ends, going part way up into the hills and then abruptly stopping.   I figured that I could pause for a few minutes of flying and get some nice aerial shots of the valley.  

Napa Valley in the spring.  Vineyards on the left and right, pasture in the middle.  

I was a bit surprised when the dead end road turned out to have two large stone gate posts.  That looked interesting, but I didn't think much of it until I started to fly my drone up the small canyon and discovered a fairly large cluster of buildings that had been long abandoned and fallen into ruin.  That was a surprise.  I was in a very rural part of Napa--what was this doing here?  


























As you can see from the image of the round building just above and the video below (link to the YouTube video), there are quite a set of buildings up this remote Napa canyon.  They're just past the stone gates--out of sight from the road, and out of mind of the good people of Napa.  

As you watch the video you see what looks like a long, rectangular building that seems a little like a castle, complete with crenelation.  Near to that is a rather large circular building that seems like it was once several stories tall.  

This spontaneous drone flight posed a mystery for me:  What's going on here?  


What's the story with these buildings? 

In particular, what's the story of that large, round building?  


The drone didn't have any EXIF metadata, so there's no map data here to share.  

However, I found that if you work just with what you see, you too can figure out the backstory here.  

What / Why / How did these buildings come to be here?  

The story I found is fascinating and deserves to be better known.  But when I ask around, I find that almost nobody in Napa or in the rest of California knows anything about this.  

Can you uncover the story here?  

Let us know what you find out... and as importantly, HOW you found it out!  

Search on!