On 22 October 1921, after twelve years on Grant St., Elder moved his bookstore to 239 Post, across the street from where the 1898 store had been. The new store offered several advantages, including a larger sales areas and a gallery & lecture hall. As an added bonus, Elder was now directly across the street from Gump’s, a family-owned, one-of-a-kind store with an international reputation.
Elder still thought of himself as both a bookseller and an art dealer. The art objects were displayed primarily in the mezzanine and stairwell. And for the first time, cash registers are in plain sight: they had previously been carefully hidden, lest they detract from the carefully planned atmosphere.
When the Grant St store opened in 1909, the Bernard Maybeck furnishings were brought over from the Van Ness store: Arts & Crafts chandeliers and stout wooden bookcases. Likewise, when Post St. opened, the chandeliers and bookcases came along, as well as the gothic window screens that Maybeck had designed for Grant St.
By all accounts, Elder made good use of his new gallery & lecture hall; over one hundred artists held exhibitions at the “Paul Elder Gallery,” and there were frequent readings by featured authors.
Presumably Elder was affected by the Great Depression as much as his customers, but appears to have weathered it well. Although he shut down the Tomoye Press in 1918, he continued to publish the occasional volume into the early 1930s.
Update 28 June 2018: I have positively identified the current Graff Diamonds at 237 Post as the former location of Elder’s bookstore at 239 Post. The clincher was the lamppost in front of the building, which also appears in a 1920s photograph of Elder’s shop.