Complex sentence: The district is currently based in San Diego County and includes Fallbrook, San Marcos, Valley Center, Escondido, Santee, Lakeside, and mountain and desert areas stretching to the Imperial County line.
Split into simpler sentences: The district is currently based in San Diego County. It includes Fallbrook, San Marcos, Valley Center, Escondido, Santee, Lakeside, and mountain and desert areas stretching to the Imperial County line.