The setting of The Underground Man in the dry California hills makes fire an appropriate physical phenomenon, with sufficient force to endanger the landscape, property, and people. The devastation it can inflict as it quickly spreads also makes it a suitable metaphor for the rampant destruction of the Broadhurst family and others associated with it. Although it is Stanley Broadhurst who actually starts the literal fire, his behavior is also presented as a reaction against the selfish wrongdoings of his father, Leo. As Lew Archer gets to the bottom of the mysteries that have emanated from Leo’s supposed disappearance, the revelations destroy more relationships but also clear the figurative landscape, allowing for future new growth.
As Archer progresses with his quest for answers, the woods are also rapidly burning. As the flames physically separate people, they stand for the gulfs of understanding and affection that keep the characters from each other. The fire that strips away the vegetation could be compared to Archer’s removing the layers of misinformation and deceit that hid, among other things, Leo’s grave. Archer himself compares the conflagration to war, as the bright flames he sees through the smoke remind him of guns flashing in the distance.