Tall straight trunks shed shaggy, papery sheaths of bark in the eucalyptus grove. The forest floor is covered with long, sickle-shaped leaves and hard, blue-tinted nuts. Young sprouts–and sprouts from mature trunks–have rounded, blue-gray leaves that are completely from those of mature trees. This is Eucalyptus (Eucalyptus globulus, Tasmanian blue gum): beautiful, flammable and invasive.
Blue gum was first planted in Marin as a fast-growing windbreaks and for a brief time as a commercial crop (though as far as I know this never was lucrative). As a native to southern Australia, it thrives in California and spreads quickly. No native plants can grow in Eucalyptus stands–either because the leaf litter is so thick, or because they are killed off by the strong-smelling oils the tree produces. The same oils and abundant shedding of bark and leaves can turn these trees into torches during a wildfire, increasing the danger for homes and people nearby; though they are lovely it’s a good idea to cut them down and stop their spread wherever possible.
There are several other species of Eucalyptus that can be found in Marin, but this is the most weedy and common.