Sodicity got us tricked . Who would have predicted the soup underneath .

While our  Savannah hill slope topsoils had some friability and stability,  little did our antecedents realize that the old  subsoil could be so unstable . Only sodium to hold the A2 horizon sand together . 
Our landscapes look and feel like concrete most of the time,  so it is  no wonder that  the subsoil  soup phase  ( A2 horizon )  is not easily seen.
Tragic for so many valleys where a drain might cut into that old layer and send the whole drainage line into meltdown, This gully on land south of Adelaide has  only a small catchment,  but the power of salt to start  the underground movement to start a rejuvenation cycle  is evident .

Are the rocks necessary ?
The usual problem is that during over grazing phases both sheet and rill erosion would have carried away the original topsoil in main drainage area .( isn't late winter spring a great time to sell grass?)





What would you do to fix it ? It looks to me that rocks seem to do little and create a nuisance.   IF , sown with lime , and well grazed this paddock will have a chance of being a useful if precarious piece of pasture.

Summary  : Rework , compact and resow with fertilizer but without rock
  Equipment : Small excavator to save topsoil , mixin  a bit of the B horizon especially and lime and compact .
Leave the trees ?   better to rework soils or leave them ? and plant new / standalone trees only where they make sense .
Not if the catchment is small .?