To find the map's scale, we need to set up a ratio between the distance on the map and the actual distance.
The actual distance between the high school and the college is 2.6 miles, and this distance corresponds to 1 inch on the map.
We can express the scale as:
\[ \text{Scale} = \frac{\text{Distance on map}}{\text{Actual distance}} = \frac{1 \text{ inch}}{2.6 \text{ miles}} \]
To simplify this scale to whole numbers, we can eliminate the decimal by multiplying both numbers in the ratio by 10:
\[ 1 \text{ inch} : 2.6 \text{ miles} \implies 10 \text{ inches} : 26 \text{ miles} \]
Now, we simplify the ratio \(10 : 26\) by dividing both numbers by their greatest common divisor, which is 2:
\[ \frac{10}{2} : \frac{26}{2} \implies 5 : 13 \]
Thus, the scale of the map in simplest form is:
\[ \boxed{5 : 13} \]