To access Frontier land on the North side of the river, you will need to 'repair' the bridge. If you follow the river to the East (right), you will find the broken bridge. Do not worry if you have difficulty finding it, there will be a goal to accompany this task (Supplies for future), and if you click on the Help button in the goal request, it will take you directly to the bridge area. Once you click on the broken bridge, you will receive the goal steps to begin repairs.
PART 1 OF 2 - BRIDGE GOAL
PART 2 OF 2 - BRIDGE GOAL
Once you have completed the "New Bridge" goal, another series will follow:
If you ran out of gold deposits before, you will now be able to access gold deposits across the bridge into 'Golden Mountain' area