HC Shaw was started in 1872 or 1876 depending on what source you use. He was a salesman who purchased the Robert Baxter Patent that was issued in 1868. There is also the Madison plow from Stockton that pre dates that plow patent # 20647 from 1858.
This article from 1889 puts the Baxter plow being built in 1864, and Shaw selling implements in 1867.
https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=PRP18890420.2.45&e=-------en--20--1--txt-txIN--------1