On Wed, 26 May 2010 07:02:43 -0700, MNRebecca wrote:

Thanks for all the input, everybody. I've sent an inquiry to the local
historical society. I'd love to know when this was built. WPA project?
Did they have this technology when my family owned the farm (1903ish to
1925ish)? I'll be in the area again for Memorial Day Weekend to
decorate the graves of family members and will try to take more pictures
then. Didn't get a single one straight across the traveling path of the
bridge!

R.

Courtesy of Google, it looks like what's referred to as a pony truss
bridge. In the early 1900s, they were the cheapest bridge design for
short spans and a number of companies made them. By the time the
depression and WWII were over, highway departments had moved on to newer
designs (than steel truss). Example of one still in use:

http://bridgehunter.com/in/gibson/2600283/

Consider the possibility that "your" bridge was repurposed from its
original use/location. As those bridges were phased out, some were
probably free for the taking.

But the best way to solve the mystery is to inquire locally this weekend.