<P> Mesquite Spring is located in the northernmost part of Death Valley . This part of the valley has numerous cotton top cactus, blister beetles and cholla cactus . On the alluvial fan above the springs there are 2 - 3 thousand year old petroglyphs from the extinct Mesquite Spring culture . </P> <P> The petroglyphs here are made possible because many of the rocks in these arid conditions have desert varnish on them . This particular form of desert varnish takes 10,000 years to make 1 / 100th of an inch of varnish and is deposited by a certain type of bacteria that collects the iron, manganese and clay needed to make the varnish . </P> <P> Also, since varnish is created at a predictable rate, it is possible to date petroglyphs based on the amount of re-varnishing that has taken place since the marks were made . Varnish does not normally form on carbonate rocks because their surfaces weather too easily . </P> <P> In a wash near some of the petroglyphs there is a fault scarp that exposes some fanglomerate which is a type of sedimentary rock which looks like concrete with large rocks intermixed . In fact it is lithified alluvial sediment . </P>

Hollywood the golden gate bridge and death valley are all located in