A Crossing of the Missouri Pacific and Southern Pacific railroads
Randy Curlin provides these photos of the Tower 138 interlocker location in Harlingen. Thanks, Randy!
"The Harlingen crossing was first automated with signals to deactivate the tower. Later it was "simplified" with stop signs in order to deactivate the signals in the early 1990s. The crossing protected the SP line running from its Harlingen yard to Edinburg/McAllen and the MP Harlingen-Kingsville line. Post 1975, SP was using the MP line so this crossing saw very light use save for a couple of locals and yard jobs. The diamonds (MP main and drill-yard lead) were removed in 1998 to speed up operations in the area. The SP switch job was moved to the MP yard and a worn out connector track allowed access for the Santa Rosa sugar mill from the MP yard."
Tower 138 Location Photos, courtesy of Randy Curlin

Above: This photo (June, 1998) is looking south toward the MP Harlingen yard.
The main is the left track and the yard lead is the right track. The SP line
crosses
from left (Harlingen) to right (Edinburg). The backs of stop signs are visible
for northbound trains. Tank cars are sitting on the MP-SP interchange tracks.
The
connector track that allows southbound trains to access the SP line for
Brownsville is out of picture to the left.
Below: This photo is looking west toward SP Edinburg. The nearest MP track is
the main and then the yard lead. Harlingen is to the south (left) and Kingsville
is to the north (right). It is strange that an SP yard limit sign is so close to
the diamond. Hopper cars are on the MP-SP interchange tracks. June, 1998

Below: UP has begun the removal of the SP line up to the diamonds. Looking
west. Oct 1998


Above: Only the roadbed remains of the former SP line. The MP tracks show
newer rails where the diamond was. Looking west. November, 1998
Below: A similar view from September, 2004 shows that grasses have taken over
the former SP alignment. Looking west.