Don, this is a page. It’s featured images are 1140×350. Every page has an id number. Hover over it in the page listing and you’ll see the id number at the bottom of the page.

I think WordPress is rather weak with this. The page id number should show up in a more obvious way since so many themes – including yours – use them.

Genesis slider settings have a place where you can put the id number of all pages you want for the slider. I recommend having special pages you use as slider pages.