Simplify the following text for a Grade 9 native English-speaking person.
Original: Because meanders only form on flat plains , the river must have formed before the ranges were pushed up ; this happened in a mountain building event referred to as the Alice Springs Orogeny which peaked between 400 and 300 million years age ( Devonian to Carboniferous Periods ) , .
Simplified: Because meanders only form on flat plains , the river must have formed before the ranges were pushed up . This happened in a mountain building event known as the Alice Springs Orogeny which happened between 400 and 300 million years ago , in the Devonian to Carboniferous Periods . .