The Barretts Tunnels were a pair of railroad tunnels built in 1853 by the Pacific Railroad, the first ones in use west of the Mississippi River. The tunnels were dug through two ridges in the vicinity of "Barretts", near Kirkwood. In 1944, the Missouri Pacific Railroad (which had taken over the Pacific Railroad) relocated their line just to the south of the tunnels, thus abandononing them.
In 1978, the nearby National Museum of Transport nominated the tunnels as nationally historic to the National Register of Historic Placed; they were indeed adopted as such. Today, while the east tunnel is barren, the west tunnel is still in use by the museum for rail eqiupment storage.
Meanwhile, the former MP line, still active, is now the Jefferson City Subdivision of the Union Pacific Railroad.
Here is a timeline of the tunnels, as submitted to the NRHP:
1856-57: Stone piers erected in west tunnel for roof support
1857-?: More stone piers, then brick piers and finally concrete piers erected
1860: Original pear-shaped 56 pound imported Welsh iron rails set at 5'6-1/2" gauge replaced by more conventional "T" shaped rails
1869: Original 5'6-1/2" gauge reduced to what is now standard gauge of 4'8-1/2"
1915: 90-lb. ASCE rail laid
1929: West tunnel reamed out and concrete portals and piers constructed and east tunnel also reamed out
1930: 110-lb. RE rails laid
1944: Missouri Pacific Railroad tracks removed from east tunnel (tracks in west tunnel remain)