Complex sentence: Wells gathered his clan and cattle together along with a young ranch hand named Frederick Russell Burnham, who Wells had trained in shooting and considered almost a part of his family, and began driving his herd into the mountains, hotly pursued by the deputies.
Split into simpler sentences: Wells gathered his clan and cattle together, joined by his young ranch hand named Frederick Russell Burnham. They began driving his herd into the mountains, hotly pursued by the deputies.