I don't know what your base training elevation is so its hard for me to say. All I know is that from sea level to 2,000 feet elevation isn't too bad. But from 3,000 feet elevation to 5,000 is a pretty big change and you will be exerting a lot more than you think. Also the thinner air will cause you to dehydrate much faster.

And this gets worse if you were to go from 5,000 feet to 7,000 feet.

We all have our share of DNFs so don't beat yourself up. It happens to pro riders too. It's just a fact of racing.

I agree that it was a smart move for you to call it quits. It's not worth getting seriously injured.

There will always be next time,