I prefer the Garmin Fenix 3. I don’t know how much gps tracking you will be doing at the mammoth but if you need you can always bring an external charging pack if there is no where to charge it when you are out and about.
The F3 I have has heart rate and tracks steps and sleep every day. I lose around 10% per day. With GPS use it is more.
For durability I wouldn’t question it. I have worn it nonstop for a year and never have I broken the screen or scratched it. There have been times I hit it and think to myself here is no way the screen isn’t cracked. Low and behold absolutely nothing. I have also hit it so hard that I bruised my wrist from the watch and it had no indication of the strike.
My background is a patrol officer so I’m not a desk jockey (yet....) and it gets banged multiple times a day.
My only gripe about the watch is it is on the larger size. But with all the things I use it for it is well worth the price tag.