To determine the angle of elevation formed where the plywood rests on the ground, we can use the inverse sine function. We begin by identifying the relevant measurements:
- The height of the stacked blocks is \( h = 2 \) feet (since each block is 1 foot high).
- The length of the plywood is \( L = 4 \) feet.
To find the angle of elevation \( \theta \), we can model the situation using a right triangle, where:
- The opposite side (height) is the height of the blocks (2 feet).
- The hypotenuse is the length of the plywood (4 feet).
Using the sine ratio, we have:
\[ \sin(\theta) = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{h}{L} = \frac{2}{4} = \frac{1}{2} \]
To find \( \theta \), we use the inverse sine function:
\[ \theta = \sin^{-1}\left(\frac{1}{2}\right) \]
The angle whose sine is \( \frac{1}{2} \) is \( 30^\circ \).
Thus, the angle of elevation formed where the plywood rests on the ground is:
\[ \boxed{30} \text{ degrees.} \]