I need to build a wooden bridge over a creek that is aprox. 15ft. wide with 6 ft. banks. any sugestions on how?

I need to build a wooden bridge over a creek that is aproximately 15 feet wide with 6 foot banks on either side. The ground is not soft at all Does anyone have any suggestions on how to build it? I want to be able to take an atv accross it. Pictures would be great as long as there are many of them and they are of the main support system. Thanks!