It's the 'green house' by Mickey Muennng, on Partigton Ridge in the Big Sur area of California: http://www.mickeymuennig.com/greenhouse.html
From what I can find out, Mickey Muennig built it in 1976 and lived in it with his family for ages (12 or 15 years in some places). He's famous for building houses that are organic and fit into the landscape. He now uses the yurt as his studio
Here's a nice alternative for your garden Ash
By definition, it's not a yurt. It's a summer house if anything.
Trust Bushwacker. I did say it was an alternative, not a Yurt.
I had a few days recently in the Yorkshire Dales (Keld) with the Green Man (Mr.Newman to you Bushwacker) and I thought we were staying at a campsite with a Yurt, I was pretty disappointed to find it was another site down the road though.