Rich soil to grow wheat, barley, and peas in the indus valley resulted from

The rich soil of Indus Valley resulted from the floods that occurred every year in the area. The water from the flood brought fertile soil with it. 
The settlements of Indus Valley were built on the river bank. The time for this civilization is around 2500 BC, and is known to have lasted for around a thousand years leaving behind a history of great civilization.