Per the 1870 census, San Antonio Township is in Los Angeles County. Wikipedia gives 33.983333, -118.216667 as the centroid of the historic San Antonio Rancho, which covered parts of modern-day Bell, Bell Gardens, Commerce, Cudahy, Huntington Park, Lynwood, Maywood, Vernon, South Gate, and Walnut Park.
Per US Genweb (see
http://www.us-census.org/states/california/teams/LosAngeles1900-T623-92.htm), the 1900 Census description of enumeration districts provides the following two-part descriptions:
- San Antonio Township (part) Florence Precinct
All that part of San Antonio Township described as follows: Commencing at the southwest cornr of T. 2 S, R 13 W, S. R. M. thence north on the range line three miles to northwest corner of Sec. 15, said Township; thence east about 2300 feet to west line of city of Los Angeles; thence south along the west line, and east along the south line of Los Angeles city to S. P. R.R.; thence east about 1800 feet to the 1/4 corner between sections 15 and 22, T. 2 S, R. 13 W. the center of Santa Fe Avenue; thence south through center of Sections 22, 29, and 34 to the S. P. R.R. thence south along the S. P. R. R. and east side of Rancho Tajuata to Township line between Townships 2 and 3 S; thence west on Township line to place of beginning - San Antonio Township (part) Fruitland Precinct
All that part of San Antonio Township described as follows: Commencing at the intersection of the Old San Gabriel River with the northern boundary of the Downey and Hellmun Truct, Rancho San Antonio; then (the desciption presented on the website ends)
The National Archives probably has a description of the enumeration districts for 1870, but the above suggests that it probably overlapped with the rancho although the boundaries may not have coincided.
The LA County Public Library or the State Library might be worth checking for a map of the township.
