as 2,000 years ago; however others believe that the last eruption occurred as early as 20,000 to 50,000 years ago. It is too young for the potassium-argon dating technique, commonly used on specimens over 100,000 years old; as the volcano is basaltic, finding a reliable source of potassium for dating purposes would be difficult anyway. No charred organic material for radiocarbon dating has been found. Lava at nearby and similarly active Amboy Crater is interbedded with Bristol Playa sediments at a depth of about 9 meters (30 feet) which are approximately 100,000 years old. Recent argon-argon dating reveals an age of approximately 18,000 years ± 5,000 years (~90% certainty) for the most recent flow. dating with chlorine surface exposure gave a somewhat similar age of 22,500 ± 2,600 years Lava flows extend to the west and to southeast of the cone, containing basalt primarily of the pahoehoe texture, with some a'a. The flows contain numerous lava tubes and caves. The cindercone volcano itself shows signs of oxidization prominent in the reddish/orange/brown appearance of much of the upper portions. The volcano is a very popular field site for geology instruction. On some weekends, it is not uncommon to find university classes and professional seminar groups around the mountain. Quarrying operations and geological survey activity also occurs at the mountain every so often. Eruptive history The volcano erupted at least three times, emptying the magma chamber below. All three eruptions produced porphyritic basalt, although rocks from the first eruptive phase are almost aphanitic. The first eruption was a basaltic flow that created the extensive lava fields visible from Interstate 40. Due to evidence from intrusive structures, it is believed that the cinder cone was formed around this time, although rocks from this eruptive phase are not present on the surface of the cinder cone. The second phase produced similarly extensive flows, while the third eruption produced substantial amounts of tephra. It is believed that most of the present cinder cone consists of pyroclastic material that originated from this final eruption. Composition The lava found around the volcano consists of a'a and pahoehoe, with considerable concentrations of olivine (weathering to iddingsite) and plagioclase. Large amounts of gypsum can be found coating rocks near the cinder cone. See also Lavic Lake volcanic field Amboy Crater Cima volcanic field Mojave National Preserve Providence Mountains State Recreation Area Mitchell Caverns Coso Volcanic Field References External links