With respect to providing information to non-local visitors, bear in mind that in both these cases the fatalities occurred in areas administered by the National Park Service which does indeed provide safety information with various warning signs, brochures, and personal contacts, among other means. This is what is posted on the White Sands website with respect to the Alkali Flats Trail, which is less than a five mile round trip -

"There is no shade or water along the trail, and summer temperatures can exceed 100 degrees F (38 ° C). Heat-related illness is common in warm weather and can be fatal. Hike during cool times"

I would bet that there were warning sign posted, which is not to say that they were heeded. A more detailed discussion of these incidents would doubtless be very instructive.