The volume \( V \) of a rectangular prism is given by the formula:
\[ V = \text{Base Area} \times \text{Height} \]
For a rectangular pyramid, the volume is calculated using the formula:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
Since the pyramid has a base and height that are congruent to the rectangular prism, we can use the same base area and height. Given that the volume of the rectangular prism is \( 252 , \text{in}^3 \), we can express the volume of the pyramid in relation to the volume of the prism.
Substituting the volume of the prism into the formula for the volume of the pyramid:
\[ V_{\text{pyramid}} = \frac{1}{3} \times 252 \]
Calculating this gives:
\[ V_{\text{pyramid}} = \frac{252}{3} = 84 , \text{in}^3 \]
Thus, the volume of the pyramid is
\[ \boxed{84 , \text{in}^3} \]