The desert's stark reticence challenges comfortable notions that we humans occupy the apex of benign, reasonable processes that have unfolded especially to produce us.
At first glance, this is not an especially stunning sentence. It doesn't really start the book off with a bang (though there is a prologue that begins with a shorter, zippier line). It also contains some fairly abstract, generic terms like "challenges" and "notions" and "processes" that in other hands could have made the sentence deadly dry.
So why do I like it? First, the striking phrase "stark reticence" at the beginning creates a lot of goodwill for proceeding through the rest. The phrase personifies the desert, and it's always nice to have an active presence for the reader to attach to right off the bat. Moreover, it brings together two terms that I, at least, am not used to seeing together. It makes me think the writer is precise and inventive, without being overly showy about it. The vividness of that phrase spreads over the relatively dull words in the rest of the sentence, and the dull words, in turn, end up setting the phrase off more. The dull words keep the prose from becoming purple, an especial risk in nature writing.
Second, although it's a somewhat long sentence, there is only one comma. As a sort of Johnny Appleseed of commas myself, I appreciate this particularly. But it's not just a matter of leaving commas out. The sentence is constructed in such a way as to not need them. It's a sentence about qualification--in fact, the whole thing is one big qualification of humanity's sense of itself at the end of the evolutionary chain. Qualifications usually beget commas. However, Wallace has obviated this problem by correctly identifying the subject of the sentence as the desert, not humanity. In other words, the sentence mirrors its point: we're not at the apex after all--not in this book, anyway.
With the true subject properly named and situated, the rest of the sentence can unfold according to the book's overall argument. And it really does seem to unfold. As we move forward through its smooth, nearly comma-free terrain, complex ideas peel away and bring us--at last and ironically--to "us." Here we are, except we don't know where we are anymore. Now we are in position for a guided tour through the "enigma" of the California desert.
(No, I haven't finished the Pynchon cinder block yet; thanks for asking.)