Bashan was the most fertile part of Gilead along the Yarmuk River in the Transjordan, and it was a byword for prosperity in agriculture and animal husbandry (Psalm 22:12). As a result, cows of Bashan
refers to the luxury that the women of Samaria enjoyed. Most probably they had an extravagant lifestyle that allowed them to indulge in sensuality and have lots of parties.1
1 “Hear this word, you cows of Bashan, who are on the mountain of Samaria, who oppress the poor, who crush the needy, who say to your husbands, ‘Bring, that we may drink!’