Complex sentence: With the 1849 California Gold Rush, a massive migration occurred to the west coast, and along with easterners came flocks of sheep and their eastern herding dogs; from the southwest came people and sheep.
Split into simpler sentences: With the 1849 California Gold Rush, a massive migration occurred to the west coast. Along with easterners came flocks of sheep and their eastern herding dogs; from the southwest came people and sheep.