Agata is using one of the modern definitions of the word "stock."
Stockdale (and its spelling variants) is a place name that is a compound word as
Agata suggested. However, the etymology of "stock" is from Middle English ("stok"), from Old English "stocc" meaning "tree trunk." The word "dale" is the Old English word "dael" meaning (as
Agata indicated correctly) "valley." Therefore, the name Stockdale means something along the lines of "valley filled with trees (or tree trunks if you want to nitpick)."