The gravel road east of Alta is a work road towards a dam and hydro plant. It will come to an end. There are only hiking trails to Skoganvarre which I would not recoomend with a loaded bike. You can see more on this detailed map: https://www.norgeskart.no/#!?project=norgeskart&layers=1002&zoom=8&lat=7757109.37&lon=841996.36&markerLat=7779168.78205541&markerLon=860559.8403970479&p=searchOptionsPanel