For those of y'all who were less than edified by wow's and TEd's helpful comments (I asked a carpenter and the size of the planks, respectively) ILedIU.

The planks are (per M-W on line) sawed yellow-pine lumber nine inches (22.5 centimeters) or wider and three, four, or five inches (7.6 to 12.4 centimeters) thick.

So there!