A diagram showing the relation between confined and unconfined aquifers; figure 5 from USGS circular 1186; <a rel="nofollow" class="external free" href="https://pubs.usgs.gov/circ/circ1186/html/gen_facts.html">https://pubs.usgs.gov/circ/circ1186/html/gen_facts.html</a>.
<p>The regions in the figure correspond to:
</p>
<ul><li>light blue zones are aquifers,</li>
<li>darker blue hatched zone is an aquitard,</li>
<li>light brown (tan) section is the vadose zone (unsaturated zone), and</li>
<li>dark brown area is "impermeable" bedrock (an aquiclude).</li></ul>
U.S. Geological Survey
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