The direct cause of these dying Euc's is the Lipid, a parasite that came from Australia 100 years ago. The trees have multiplied uncontrollably until now. the reason is that water devoid of trace amounts of oxygen cannot be used for photosynthesis so the sap the Lipid drinks from the tree cannot be replaced. Nightly condensations are taken up by the tree from fine feeder roots at the base of the tree after moisture runs down the trunks.
Below you can see the black stains of the carbon.
These Oak trees are on HWY 192 just east of Mission canyon. The stand has been historically very healthy. Now they are dying.
Eucalyptus finally cut down along 101