No excuse. Do these people not know that snow and ice are slippery?
For many people in California, (and a very large portion of this planet) the notion of snow or ice on a road is in the same realm as a paranormal event. You may as well tell them how to prepare if they happen to wander into a haunted house.
we knew enough to bring extra water and proper attire--not flip flops and wife beaters.
That's because you were a tourist who had the resources and time to prepare for and research what you were going well out of your way to visit.
Death Valley didn't come to visit you in your native area of four seasons. You visited Death Valley. And as the ominous name implies, it is a place where people can very easily die.
There is no reason to pat yerself on the back for being smart enough to properly prepare yerself to go out of yer way to visit a place or environment with "death" in it's name.
If anything, to purposely and intentionally visit a place like that sounds about as smart as urinating on an electric fence.