I found all of the below stamps in a five-block area south of Wilshire and just west of the 110 Freeway. I look forward to further exploration of LA because based on this small expedition I bet there are hundreds of different stamps there.
Clark & Niemann Contractors, 108 S. Broadway, Bixel Street
Clark & Niemann Contractors, 108 S. Broadway, West 7th Street
F. Gillespie, Inspector, Garland south of 8th Street
You can see the size of these tiny "inpector" stamps, next to my shoe. Gillespie may have moved from inspector to contractor, or vice versa, or been part of a family operation...
F. Gillespie, Contractor, Garland south of 8th Street (contrast heightened slightly for readability)
F. Gillespie, Contractor, Garland south of 8th Street
Griffith Company 1930, Hartford between 7th and 8th
Griffith Company, 1934, Valencia Street north of Wilshire
Note that this stamp is identical to one used in San Diego in 1948.
L.M. Hopkins, Contractor, Hartford between 7th and 8th
C.H. Johnston, Contractor, Garland south of 7th Street
C.W. Johnston, Contractor, Garland south of 8th Street
I can't tell if C.H. Johnston and C.W. Johnston are the same with a typo, but I can't imagine a typo in concrete.
Kancuse City Inspector, Hartford between 7th and 8th
City of L.A., Hartford between 7th and 8th
City of L.A., Hartford between 7th and 8th
City of L.A., Hartford between 7th and 8th
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