Original: While Palmdale is still a part of Los Angeles County, the urbanized centers of Palmdale and Los Angeles are separated by the San Gabriel mountain range, which is about 40 miles (60 km) wide.
Simplified: Even though Palmdale is in Los Angeles County, it is not connected to the larger Los Angeles population area. It is separated from it by a mountain range called the San Gabriel Mountains that are over 40 miles wide and almost 2 miles high overall.