And were some of those parts buried 30 feet deeper in the soil?
I don’t recollect the circumstances for depth provenance of Lucy’s parts. Depth matters, of course, but the stratum (layer) the remains came out of is more important; items within a stratum can become mixed within that layer by water and wind as well as by other influences. Even though remains can be moved considerably by environmental means, the stratum they came from can be determined by the minerals that become part of the fossils. Items from varying geological strata are traceable to their original stratagraphic location.
Fossils like Lucy are in fact minerals which come from the strata they were deposited in. Fossilization starts after fifty years of weathering and continues until the remains become all mineral.