Radiocarbon dates from Wrangel Island, north of the Siberian coast, place mammoths there until roughly 4,000 years before present. The Great Pyramid at Giza was completed around 4,500 years ago, so the two overlap. A separate late population on St Paul Island in the Bering Sea persisted to about 5,600 years ago before failing, apparently as its freshwater lakes shrank.
The Wrangel animals were isolated when rising post-glacial seas cut the island off from the mainland. Genome studies of that population show the signatures expected of long isolation at small numbers: reduced diversity, loss of variation across large chromosomal stretches, and an accumulation of probably harmful mutations.
A persistent misconception is that these late mammoths were dwarfs. Wrangel individuals were only modestly smaller than mainland woolly mammoths. Genuinely dwarfed forms did evolve elsewhere, notably the separate species Mammuthus exilis on the California Channel Islands, but that is a different lineage.