The 1st California was one of four regiments that made up the "California Brigade" commanded by Colonel Edward D. Baker, U.S. Senator from Oregon and close friend of President Lincoln. In April, 1861, Baker helped to organize what was intended to be a single regiment to represent California in the Union Army. The response was so large, however that four regiments were created and numbered 1st, 2nd, 3rd, and 5th California (there was no 4th). As most of the recruiting was done around Philadelphia, the Governor of Pennsylvania objected to those men not counting in his state's quota of volunteers, and had these four regiments renamed the 71st, 69th, 72nd, and 106th Pennsylvania following the death of Colonel Baker here. Thus, the "California Brigade" became the "Philadelphia Brigade."
There are numerous accounts of Colonel Baker's death but no historical consensus or definative version. Confederate veteran Elijah White accurately summed this up when he wrote, "General (sic) Baker was killed ... no one knowing really who did it, although there was much romancing at the time."