If you had all your family's worldy possessions and supplies for a long trip inside a wagon, do you think a couple of horses or oxen could haul it up a mountain? Minnesotastan explains how it was done, at TYWKIWDBI. Link
(Image from the book Hard Road West, by Keith Heyer Meldahl)
Once they reached the Nevada desert--with considerable difficulty--they jettisoned as lot of it. Later emigrants said that they could follow the discarded pianos, chairs, barrels, etc., through the desert. Scattered among the litter were the graves of the many killed by various diseases.