The Central Valley in California is located between the Coast ranges and the Sierra Nevada, running roughly parallel to the pacific coastline. Rather interestingly it has an "entrance" at the San Francisco Bay to the oceans. This entrance together with the rather low elevation of the region, the valley is rather vulnerable when the level of the sea rises.
The recent situation is shown on the figure above with major cities and major highways shown in their current location. It can be clearly seen that the ocean has found its way to the inside of the valley through the neighboring ranges, and it reaches almost the Stockton area.
Now what happens when the sea level rises by only 5 meters (16 feet)? Next figure show this situation, when the outskirts of Sacramento are under water already, together with Interstate 5.
Let's raise the sea level by an additional 5 meters. Half of Sacramento's are is washed away and the waves reach further inside the valley. Remember that this just by adding 10 meters or 33 feet to the current sea level.
The last figure shows the sea level if it is 25 meters above the current one. Cities and highways are represented at their current location for reference.
The above maps had been derived from the Shuttle Radar Topography Mission elevation dataset.