I have watched a few different herds of cow elk over the past 5 summers in Central Utah and it seems that the mature bulls move in to the area where the cows are the last week of Aug and in the first week of Sept the bulls really start to mix in with the cows for the rut. Spikes seem to be alone during the calving season, but move back into the herd around the end of June. Semimature bulls 2-3 years old seem to move into the herd the first part of July. Mature bulls seem to summer away from the cows and young bulls. That is just what I have noticed the past few years, checking on the herds weekly.