I think it’s a juvenile falsa crucera de hocico respingado, minus the red bit on the tail. Here’s my visual snake identifier: dbosk.com/snakes.
Fun note about my snake page: it’s simple, but serves a purpose ignored by the 1990s-style Serpentario site it links to – allow you to identify a snake you see. ¡Que concepto! I recently sent the code to them, saying they were welcome to it, and they replied thank you, we’re planning an upgrade to our site soon.
I don’t still have their email from eight years ago, but they said exactly the same thing then.
Reminds me of this t-shirt I probably should have:
That is a fast snake! Glad you captured a photo of it. Bravo!