CABRILLO Historic Structures Report

Figure 16. The missing metal observation slot shutters are located inside this structure.

BASE-END STATION, BATTERY MCGRATH (Preservation)

Location

This structure is located just below the Cabrillo statue, on the east side of Point Loma.

History

This structure served as the sole fire control point for Battery McGrath, the only Endicott battery incorporated into the updated harbor defenses. Constructed c.1920, this station was part of a remote network that tracked targets and relayed the data to their associated guns via a plotting room. Observers in these stations used sophisticated data collection instruments that improved the coastal gun aiming system. Originally temporary structures, by WWI concrete walls and tar and gravel roofs provided permanence. During WWII the tar and gravel roofs were replaced with earth-covered rough aggregate concrete roofs. Cemented boulders on the roof provided additional camouflage. The station was abandoned in 1942.

Description

Exterior

The base-end station for Battery McGrath is identical to the base-end station and battery commander station for batteries Calef and Wilkeson, except that the structure has a steeper roof slope (figure 16). The structure was also painted a drab yellow at one time.

Interior

The interior is identical to that of the base-end station and battery commander station for batteries Calef and Wilkeson, except that it has a small storage compartment built into the rear wall (figure 17). The steel plate door for this compartment is missing, although the hardware remains. Olive drab paint once covered the interior concrete. A speaking tube running to the nearby 'old restrooms' remains in place, although the restrooms are now in ruins.

Condition

Exterior

The concrete is in good condition with some cracks and exposed reinforcing bar. The steel surface hatch is extremely corroded with holes and missing parts. The asphalt waterproofing is worn and stones have dislodged, leaving voids. Exposed reinforcing rod and spalls mar the main observation slot. Covered with temporary wooden slats, its removed metal shutter is stored inside. At the south observation slot, the header is cracked and the metal shutters corroded. Vegetation has rendered the hatch inoperable.

Interior

The interior walls feature several concrete spalls: spalls caused by rusted ferrous metal near the concrete surface; minor spalls at metal attachments; and a severe spall at the southeast corner opening. These walls were originally painted, but only fragments of the paint remain. Graffiti and corrosion stains from metal attachments are present on the walls. Ghosts of items no longer present on the south wall are apparent.

Structural Analysis

The spalled concrete and exposed reinforcing rod at the front and side areas of the roof appears to be a consequence of casting the large stones into the face for camouflage. The deterioration at the front and sides of the roof appears primarily as a result of shrinkage over time of the concrete surrounding the large stones. This shrinkage would have caused cracks around the stones, which would have then allowed water, salts and air to penetrate down to the rebar. The reinforcing rod would have then begun to corrode, and the resulting expansive forces would then have spalled the stones. The only structural concern is that this deterioration reduces the capacity of the anchors that support the steel shutters. The cracks at the interior concrete surfaces are relatively minor and do not at this time appear to compromise the structure's capacity.

Figure 17. Unique to McGrath's base-end station, a storage compartment is present on the rear wall.