Mr. Eagle - deep in the wood and not visible from up the creek at the road edge

In my haste to get a shot of our national bird I stepped over the guard-railing and almost onto one of the largest snakes I have caught a glimpse of in decades - it immediately disappeared into the grass and brush but remained about three feet from my feet giving an ominous rattling sound with the covering grasses quavering away - I got a slight photograph of it but found it hard to identify until it went slithering away when I prodded it with a stick - it was a dun gray and about six feet long, and maybe four inches in diameter  - either a common black snake or a water moccasin - but I will never know for sure - and even though I have no snake phobias to speak of, I definitely was a little leery of continuing on to the creek in the grass.  However I plodded on, thrusting a long stick ahead of me into the grass to startle any more Serpentes and arrived at the creeks edge only slightly ill at ease.