Yes Elk do eat cottonwood trees.
Cottonwood Trees are one of the Elks favorite types of trees to eat on and so if you have cottonwood trees in your yard and have Elk then expect some damage to the cottonwood trees if the Elk come up to them.
Elk find Cottonwood Trees to be very appetizing.
Elk also like to eat on Juniper Trees and also love to eat Juniper Berries as well.
Elk do love to eat Juniper Berries and if the Elk is in a location where Juniper Berries are the Elk will eat those Juniper Berries.
Most Elk Eat Juniper Berries during the winter months but they can eat them at any time when they need too or come across them.
Deer also eat Juniper Berries in areas where Juniper Berries grow.
Elk also eat things such as trees, shrubs and other plant-based foods but Juniper Berries are on the list of things they eat.
They may also eat other plants such as garden plants as well if you have a garden in your yard and have Elk or deer you should protect your garden and plants from the Elk and Deer.