Looks more like and more likely to be a Red-bellied Black Snake, due to habitat and the fact that it was basking in the sun. How long do you estimate it was?
I could not see any red on it’s lower scales, as is usual for Red Belly Black snakes, which is why I opted for the Cryptophis ID. The length is estimated to be around 1 metre.
The head shape with what appears to be a distinct cathus rostralis, is more like a Red Belly than a Small-eyed. The reason that you didn't see any red is because it may have been in pre-slough, as I can just barely make out what appears to be a milky eye. It also seems to be flattened out, which is more typical of a basking RBB. Image quality is such that a 100% positive ID is difficult. Perhaps a third opinion on this would be helpful.