Third-Day Road Log: From San Ysidro to Gilman Tunnels and Soda Dam
— Karl E. Karlstrom, Laura J. Crossey, Cameron C. Reed, Ben Rodriguez, Spencer G. Lucas, Shari A. Kelley, and Fraser Goff

The Third-Day Road Log consists of two ~2-hour stops at Gilman Tunnels and Soda Dam. We drive from San Ysidro into the Jemez Mountains along State Road 4. From San Ysidro, we follow the Jemez River past Jemez Pueblo, turn left on State Road 485, drive to Gilman Tunnels, then back to State Road 4, and make a left to Soda Dam. The goals of this field trip are to look at the oldest and youngest rocks in the Nacimiento nexus area. Stop 1 will discuss the Proterozoic asement of the Nacimiento Mountains uplift exposed in a fault block in the rugged Guadalupe Box of the Guadalupe River near GilmanTunnels (Fig. 3.1). Stop 2 will discuss Quaternary travertine at Soda Dam, including rocks that are still forming today. An optional stop along the route that could be done on a longer trip is the Jemez Springs Bath House to view geothermal waters.