Interesting. I'm curious about the town marked as Iowa Tract north of Cucamonga. Does it correspond to anything today? Also, the carriage drive map shows Pomona in LA county, but in the Southern Pacific map it's in San Bernardino. Did the line shift after Pomona was founded?
The SP map is wrong. Pomona is and always has been in LA County. Note that the SP map shows Pomona considerably closer to San Bernadino and farther from Spadra than the carriage map does, so the error is most likely a misplacement of where Pomona is on the SP map.