Thank you to Cathryne Bruce-Johnson, D-11 Public Information Officer at California Department of Transportation, for providing the answer to this question! Check out all the guesses here.
What is this structure located between the east bound side of the Coronado Bridge and the golf course?
Answer: From Cathryne Bruce-Johnson-
"The structure pictured in the photo you provided shows an observation tower on the west side of the highway that was used years ago by supervisors to monitor toll collection and observe traffic conditions near the bridge. The tower also featured a ventilation system that pumped fresh air from near the golf course into the toll booths for the benefit of workers. Caltrans is planning to remove the tower, but there is no definite time line yet in place.
It may be interesting to note that there was a second observation tower on the east side of the highway that was dismantled to accommodate construction of a High Occupancy Vehicle lane.
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