LL really only approached this topic three times in the plot of a story (as opposed to possibly just mentioning it in passing). Haunted Mesa, The Californios, and the first "chapter" of Lost Treasures Volume One "Jeremy Loccard." Jeremy Loccard was intended to follow up on those other worldly aspects of The Californios.

When it comes out, you migt also enjoy the Lost Treasures edition of Haunted Mesa which described Louis's adventures and hardships in writing that novel as well as a couple of different attempts to attack the story with slightly different plots.