This is an incredibly long pony truss. I added a couple links to photos on the links section.
Better get up there to see it soon. The bridge receives heavy traffic daily with oil field and heavy farm machinery, and the boards are coming up and scattering. You can see the river below through the missing planks of the bridge. It is better to come to the bridge from the paved Oklahoma side, because the Texas side sandy road is in very poor repair and one could easily get stuck in the deep sand if you have to pull over to let the big trucks go by on your left. I was praying all the way, really! It seems like you are a hundred miles from nowhere. On a scale of 1 - 10 I would give it a 6 for challenge.
Bridge design is Warren Half-Hip Pony Truss w/verticals (light duty construction). Not a Through Truss design as stated above.
This bridge was once the southern terminus of State Highway 30. As far as I can tell it never connected to a state highway in Texas.