This is my first remodel attempt and I would like to create a doorway between a bedroom and a walk-in closet. The existing wall between the two rooms is a load-bearing wall. After removing the sheetrock, I see that the existing configuration is actually a remodel from a previous floor plan where a doorway used to be in almost the same place that I would like to place my doorway.
I would like the shift the doorway a foot or two to one side, however, I see that there is a concrete piece under the base plate (see picture below).
What is this concrete piece and can it be removed?