Final answer:
The most likely soil order on the South Island's West Coast is Podsol, which is formed by leaching of minerals and organic matter due to heavy rainfall and acidic conditions.
Step-by-step explanation:
The soil order that is most likely to occur on the West Coast of the South Island in New Zealand is Podsol. The West Coast has heavy rainfall due to the prevailing westerly winds and the mountains of the Southern Alps, which create high precipitation. This results in the leaching of minerals and organic matter from the soil, making it acidic and forming Podsols.