There is is a restored heavy coast defense site at The Golden State Nation Park north of San Francisco. IIRC this contains a 16"/45 gun.
Coastal Artillery was a US Army service branch, well-developed from WWI on. The Golden Gate fortifications were well-developed, they included AA, extensive minefields & minefield-maintenance ships (ACM types that were owned & operated by the Army).
My fave is Fort Drum, the 'concrete battleship' built over El Fraile Island east of Corregidor, w/ 2 x dual 14" battleship turrets, 4 x 6" armored casement mounts, a pair of open 3" AA mounts, & a tall lattice-type mast for spotting & searchlights. Construction was begun in 1909, & finished ~1914. Quite a bit of Navy expertise & ordnance was incorporated into this Army fortification. I've read that the max. range of the 14" guns was limited by their turret's max. elevation of 15 degrees.
Haven't read much about the Canal Zone, but they were also v well-defended.
My family vacations annually at Cape May, NJ, where a few remnants of the forts protecting the entrance to Delaware Bay remain (an observation tower, & an ammunition-storage casement). IIRC, the Cape May ordnance included 4 x 6" guns, but their sites were destroyed by seacoast erosion.