What Is This Structure Near Sunnyside? [PHOTOS]

I drive by this structure along I-82 everyday on my commute and I've never seen anyone or anything near it, it looks like a rodeo arena but seems rather small.

Do you recognize this structure and know what it's used for?

I took some pictures this week. It does seem odd the way it's built, as it doesn't seem very flat where the Porta Potties are.

It makes you wonder what the facility is used for.