We saw two very smooshed snakes on our ride yesterday. DH thought one was a rattler, but I think more than likely it was a hognose. Kind of hard to tell when they're upside down and flattened and icky (and just generally "orangish").
I'm sure if you did a google image search on black texas snakes, you'd come up with your friend. I tend to lean towards the common for sightings other than the exotic. I don't know the range of black snakes - there are several types, I think - but chances are good you saw one.
Smart to keep your distance when you don't know what you're dealing with, but keep in mind that snakes are valuable members of the ecosystem and they're just out there doing their thing.