Those are remain from ppl dying on a single site through 2 different widely spaced period of time.
If this place was a road point (like the silk road), it will explain the vast disparity of orgins.
Then you have a single geographical site in montaneous region where catastrophic events can be cyclics:every x hundreds of years the soil is so soaked that the terrain collapse every time it rains more than Y MM of precipitation... Etc...
So, if this place was on an acient road traveled by various ppl crossing the area and that some catostrophical events happened spanned across a wide range of time, you'll happen to get the same relics of ppl apparently traveling together (when they were not).
It's only a problem of time base and what relevant ratio (frequency) you use. A fairly commune type of problem in Fluid flows analysis.