Request for Info on Alpa, Norway

On my grandmother's petition for US citizenship, she listed "Alpa, Stigens, Prestigjeld, Norway as her husband's birthplace. I cannot find this town and do not understand how the towns, counties, etc. relate. For example, is Stigens a city and is Prestigjeld a county or district or what? I will appreciate any help in this area as it is key to writing my mother's biography. Thank you. Jeff.