Complex sentence: Mystic Lake is an ephemeral lake in the San Jacinto Valley of western Riverside County, California, located east of Lake Perris, between Moreno Valley and San Jacinto.
Split into simpler sentences: Mystic Lake is an ephemeral lake in the San Jacinto Valley of western Riverside County, California. It is located east of Lake Perris, between Moreno Valley and San Jacinto.