Just to clear up a few things. The French Tourists died hiking the Alkali Flats trail. A remarkable hike that crosses the center of the dunes in White Sands National Monument. This
photo I took shows what it is like a couple of miles from the trail head. The trail is marked by a series of metal posts in the dunes. Lose track of the posts and you will have a hard time finding your way back. Note the three people in the distance for scale. There is no shade or water available anywhere on this route. It is not a hike to be taken lightly even in cool weather.
The trail head is just a parking area and a sign that gives ample warning of the dangers of this hike. It isn't staffed by rangers.
ETA: If you plan on hiking in any National Park or Monument, stop at the visitor's center first. They will help you pick a trail that is within your ability and advise you on what to expect.