Complex sentence: Until the arrival of the railroads the town's economy was based mainly on farming and ranching, although there was also some mining activity in the region, including a vein of asphaltum that was mined between 1892 and 1914.
Split into simpler sentences: Until the arrival of the railroads the economy was based mainly on farming and ranching. There was some mining activity in the region, including a vein of asphaltum that was mined between 1892 and 1914.