To find the area of the square baseball infield, you can use the formula for the area of a square, which is:
\[ \text{Area} = \text{side} \times \text{side} \]
Given that each side of the square measures 30 yards:
\[ \text{Area} = 30 , \text{yards} \times 30 , \text{yards} = 900 , \text{square yards} \]
Therefore, the area of the baseball infield is 900 square yards.