The elevation of Chicago, Illinois above sea level is 600 feet
The elevation of Desert Shores, California is 800 feet less than the elevation of Chicago.
Therefore, the elevation of Desert shores in real values would be (600 - 800) feet, this equals -200 feet.
Note that the elevation of Desert shores from the sea level is negative. Negative elevation means depression.
Hence, we can say that Desert shores is 200 feet below sea level.