Hey Rod you have been fishing there all this time and that's the first snake you saw. Does not look like a gopher snake too me. There are lots of rattlers along the Thom generally they will here you and hide before you see them (Don't stick your hand in places you can't see). They do swim and like it in shaded areas around the waters edge (more food sources there). Generally they hunt at night so it's a good idea to have a light on your hat so you can see them and give them their space; they get real upset when you step on them. I know I stomped on a rattlers tail once to see how fast they are back when I was young and stupid. The guy who taught me about snakes told me that in that area you probably walk over 30 a day; they pick up sound vibrations from your foot steps and go under ground to avoid you. Thirty five summers fish that region and I have never been bit, so I can tell you from experince that you don't need to fear the snakes. The other snake you will see up there is the bull snake also known as the rubber bowa. These guys are non venomous but do bite and can be aggresive if you anger them; unlike the rattlers who will retreat if given the chance bulls have been know chase aggressors off.
Nice report Rod and i recognise that section of river by Ashcroft, fished ther many time.