Rattle Snake

We were walking along the old railway trail near Deep Fork Wildlife Refuge not for from Okmulgee in Oklahoma,we then went onto the boardwalk that over looked the river, as we walked onto it my husband noticed the snake, it was under the bench, if we had not seen it and sat down it could have been a different story, its tail started to shake & its head came up as if was going to strike, we backed off.