Complex sentence: It is described in the Antioch Sand Dunes, which formerly occupied a considerable acreage along the Sacramento-San Joaquin Rivers.It is now a small highly disturbed area under the threat of complete destruction.
Split into simpler sentences: It is described in the Antioch Sand Dunes, which formerly occupied a considerable acreage along the Sacramento-San Joaquin Rivers. The Sacramento-San Joaquin Rivers is now a small highly disturbed area under the threat of complete destruction.