The flooding had its beginnings in heavy rain in March 1900[1] over a very broad area extending from North West Cape to the southeastern corner of the state.
[2][3] During April and May, the rain was associated with what was described in the press of the time as "a gentle easterly flow"[4] but today is recognised to be a northwest cloudband.
The heaviest rainfall of all occurred in the Pilbara during the middle of the month,[5] and resulted in rivers such as the Gascoyne, Ashburton and Murchison overflowing their banks for extraordinarily sustained periods.
So heavy indeed was the rainfall that the normally arid "North West" (as the region was known at the time) was completely boggy and the primitive horse-drawn carts could not traverse the country not only in April, but well into May, especially as another major rainband affected the State early that month, with Onslow recording as much as 9.31 inches (236 mm) in a day on the third.
The busy Easter mail services were most severely hit of all, with the mail vans from Perth bogged down at Peak Hill after crossing a Gascoyne River that was supposedly 3 miles (4.8 km) wide as the rain extended at the end of Easter to the Murchison River’s basin.