This should be horror but it would only let me chose mystery…. I watched this about 13 or 14 years ago on TV.  I suspect when shadow lane had just come out  (If you live in BC I’m sure you’ll remember  the movie stations that were free when they came out).

A family ( mom dad and two kids I believe) takes a wrong turn and ends up in this old abandoned mining town ( it’s not exactly a wrong turn as I believe the gas station attendant was in on it.  Someone changes a sign and that’s how they take the wrong turn). the father I believe was happy to explore the town only it’s not so abandoned.   Turned out people who lived in said town didn’t want to leave fled to the tunes (mine shafts) when nuke testing started (it’s years later now though or they would have you believe.)  Anyways one of the kids falls into this shaft and finds a pile of clothing (we now know this wasn’t just an accident).     I remember a field of old cars shown from above at one point (all prev victim vehicles I assumed at the time).  I also remember a giant white almost glass like crater that I always assumed was made by the nuke that was supposedly tested.