With Charles Ross on the cusp of the completion of a nearly five-decade-long project—Star Axis, an observatory or temple to stars and light—in the desert of New Mexico, Rule Gallery presents two early, more modestly scaled sculptures from the artist’s ca. 1965–68 “Prisms” series: Broken Pyramid and Untitled (Beam), both 1968. The pair were conceived three years before his epic Land art construction ever came to mind. And these siblings, in their strange humility, are beautifully prophetic of the large ambition to come.

Each prism—an exquisitely modeled block of glass displayed on a white-metal