For I did the walk there recently I now want to present the local peculiarities of the Great Wall there. Some good photos have been shown here so I only post not yet shown items.
The Wall eastward of the Yellow River has the following characteristics:
1. It had _completely_ been covered by a basement of smoothed Stones (limestone, granite, sandstone) and by bricks. The brick layer on top of the wall is often still there. The covering bricks of the flanks are mostly removed by local farmers, who built their villages using them. Local people of about the age of 35 told me "when we were young the Great Wall looked much better (women xiao de shihou zher de changcheng geng piaoliang)" and they complained that farmers are widely destroying the surface of the Great Wall. It seems that in about 50 years the Great Wall there had more damage than in 500 years before. The condition of the Great Wall is the better the more it is away from villages.
2. The beacon towers are compact and mainly made of loess, sometimes with layers of stones.
3. On the section from Laoniuwan to the junction of inner and outer Shanxi Great Wall there are 4 beacon towers of the Hebei style (made of brick, rooms inside, windows).
4. The most characteristic item are the round becon towers on the inner side of the wall. They are always round, they are always surrounded by a wall, they did not have any built-in appliance to scale them. Some of them have a tunnel inside going up but those had been made by shepherds or farmers. I am pretty sure that these beacon towers had not been covered by bricks but the top of them should have been. The function of these towers is clear: they are always on the most prominent places and in the optical range of each other. Those had been signalling towers. Maybe also the place where the commanders were living. The surrounding wall should have had a gate but I did only find smoothed stones as a proof. Today the interior of this wall is always used as a small field.
5. On the inner side of the wall are a huge amount of this beacon tower type but often very far away. There are also fortresses around, they thend to get bigger as farer the get from the wall. It is clear, that they had been a part of the alert system.
6. The erosion ravines started to be a problem in the Ming aera. On three locations the path of the wall was corrected due to erosion.
7. The wall and the landscape there are by far the most beatiful I have seen of the Great Wall so far.
Some photos to show what I stated:
Loess wall of sometimes bad condition:

An erosion ravine, not easy to walk through.

A fortress.
Smoothed Limestone cover on the lower Great Wall.

Intact brick layer on top of the loess wall.

The most typical item of the Laoniuwan section: The round beacon towers.

-chinoook