For those only marginally interested in geology and topography, this is a difficult read, though it is well worth sticking with it. I myself read it in chunks, only a single chapter at a time, since any more tested my patience. The writing is superb, however, and the information imparted is both instructional and fascinating. When McPhee writes seemingly simple sentences such as, "There were orchards of carobs, figs, and pistachios, and an understory of prickly pears," he paints an entire countryside in just a few strokes of language. What he does with the drier subject matter of basalt and limestone is extraordinary.
Assembling California is no different. McPhee starts in the Sierra Nevada with geologist Eldridge Moores and ends on the San Andreas fault during the Loma Prieta quake. Throughout, McPhee explains that California is actually an accretion of exotic terrains that tectonically migrated throughout the eons. I'll admit that on rare occasion some content rendered me a bit glassy eyed, but the majority of the writing was excellent and the San Andreas fault section was beyond outstanding.
Taken as a whole, Assembling California is a distinguished finale to McPhee's Interstate 80 geology series that began with Basin and Range and later became a compilation entitled Annals of the Former World.