Much of the Great Plains became open range, or rangeland where cattle roamed free, hosting ranching operations where anyone was theoretically free to run cattle. In the <answer>spring and fall</answer>, ranchers held roundups where their cowboys branded new calves, treated animals and sorted the cattle for sale. Such ranching began in Texas and gradually moved northward. In 1866-95, cowboys herded 10 million cattle north to rail heads such as Dodge City, Kansas and Ogallala, Nebraska; from there, cattle were shipped eastward.
when did ranchers usually have a cattle round up?
spring and fall