During the California Gold Rush Matthieu attempted to make his fortune transporting provisions and mercantile goods to the mines. Matthieu unfortunately fell ill on the way and wound up losing all 14 mules and the goods they were packing during his sickness, thereby dealing him a heavy financial blow. He also schemed on making use of Native Americans as mineworkers, but scurvy and diarrhea lead to massive deaths among the first party accompanying him to California and the plan fell to nothing.