I want to say it was outer limits or something along that genre. It was probably in the early 90's, it was live action in color. It may have been one of those types of shows that had multiple stories in one episode.
All I remember was there were 3 people probably in there early 20's, I think it was 2 men and one woman.
They were in a secluded forest and decided to split up and go exploring when the girl came across a sand pit in the middle of a nice green forest.
Later on when the girl never returned, the guys found her in the middle of the sand pit and she aged like 70+ years and warned the guys to stay out of the sand. After they got help and notified the authorities, they show a helicopter flying over the sand pit to drop concrete over it to cover it up.
That's about all I remember!