Born of mud and ice, these unstable hills of sand, silt, and gravel were bulldozed and compacted by glaciers that obliterated much of the geological record before the Holocene.
(gravel; were bulldozed; ) (gravel; compacted; by glaciers that obliterated much of the geological record before the Holocene)
gravel gravel
were bulldozed compacted
by glaciers that obliterated much of the geological record before the Holocene