In any case look for puncture signs in the part of the roots exposed to the air and lower trunk. This could signal the presence of Scyphophorus yucca, that look

In any case look for puncture signs in the part of the roots exposed to the air and lower trunk. This could signal the presence of Scyphophorus yucca, that looks like this guy: http://bugguide.net/images/cache/YRI/QCR/YRIQCR7Q9R90OQ40JQM0OQP0Z0P0R00QS060DQ80K020DQYKTR0QDR60S040VRLQURRQ3RP0L090S0U000P0R0W0H0W0.jpg http://bugguide.net/images/cache/YRI/QCR/YRIQCR7Q9R90OQ40JQM... The larvae of this weevil can make burrows in the Joshua Tree and eventually kill your tree.