Simplify the following text for a Grade 5 native English-speaking person.
Original: The western Riverina is presumed to be a continuation of the Ballarat and Bendigo geological zone while eastern sections are underlain by western portions of the Lachlan Fold Belt .
Simplified: The western Riverina is thought to be the end of the Ballarat and Bendigo geological zone . The eastern part is over the top of the western part of the Lachlan Fold Belt .