To determine the speed of the squirrel in miles per hour, you need to divide the distance it traveled by the time it took.
In this case, the squirrel ran 9 miles in 1 hour. The appropriate expression to calculate the speed is:
\[ 9 \text{ miles} \div 1 \text{ hour} \]
So the correct answer is:
9 miles ÷ 1 hour