Where is this plant growing?

That looks like a member of the cucurbit family, Cucumber, melon, squash.

Yep, if toward the GreatPlains or SouthWest, I'd say buffalo gourd.

Coyote Gourd ... if you like it, it's not a weed. It makes a nice easy-care ground cover. Comes back from a tuber every year, very drought tolerant.

http://en.wikipedia.org/wiki/Cucurbita_foetidissima

Thank you for identifying this vine. It's growing in an empty low in southern California.