Complex sentence: The northern part of the Parris Block north of the Santa Ana River has been mostly buried by the sediments from the Transverse Ranges as they rose over the last 2-3 million years.
Split into simpler sentences: The northern part of the Parris Block lies north of the Santa Ana River. It has been mostly buried by the sediments from the Transverse Ranges as they rose over the last 2-3 million years.