There are hardy hibiscus, and there are also tropical hibiscus. I'm thinking that one might be a hardy hibiscus flower - they do grow very large flowers and I've seen them that color before, too.
Something like this:
Hybrid Hardy Hibiscus (Hibiscus Luna™ Rose)
Also lots of people keep tropical hibiscus as house plants and put them outside in the summer. Where did you get that flower, anyway? Was it on a bush in the ground or on a potted plant? Here's another with flowers that look very similar to yours.
Hardy Hibiscus (Hibiscus moscheutos)
