In the spring in Nebraska and Wyoming the travelers often encountered fierce wind, rain and lightning storms. Until about 1870 travelers encountered hundreds of thousands of bison migrating through Nebraska on both sides of the Platte River, and most travelers killed several for fresh meat and to build up their supplies of dried jerky for the rest of the journey. The prairie grass in many places was several feet high with only the hat of a traveler on horseback showing as they passed through the prairie grass. In many years the Native Americans fired much of the dry grass on the prairie every fall so the only trees or bushes available for firewood were on islands in the Platte River. Travelers gathered and ignited dried cow dung to cook their meals. These burned fast in a breeze, and it could take two or more bushels of chips to get one meal prepared. Those traveling south of the Platte crossed the South Platte fork at one of about three ferries (in dry years it could be forded without a ferry) before continuing up the North Platte River Valley into present-day Wyoming heading to Fort Laramie. Before 1852 those on the north side of the Platte crossed the North Platte to the south side at Fort Laramie. After 1852 they used Child's Cutoff to stay on the north side to about the present day town of Casper, Wyoming, where they crossed over to the south side.