Summer may be coming to an end a little sooner this year, as indicated by an even split between fiction and nonfiction in this week’s top 10 list of bestselling books in Petaluma. Compared to last year at this time, when many businesses were still closed and readers were grappling with real-life horrors by snapping up books about politics and race, the summer of 2021 has given rise to a number of flat-out seasonal beach-reads, the kind of fictional fluff and escapism that used to be the norm every year as people grabbed a book to take with them on vacation.