This is in quick answer to Stephan and Ron's queries:

The metal piece is part of CA-SBA-3725H, the NTU mine. The site was recorded 
during a survey for the current oil field development in 2003 by a different 
company, under the California Environmental Quality Act (CEQA) regulatory 
framework. The site was recommended as eligible to the California Register 
of Historic Resources. Mitigation measures included avoidance and HABS/HAER 
photographic documentation of above-ground structures (preferred), and 
monitoring and a program of testing for subsurface deposits for locations 
where ground disturbance could not be avoided.

Development of the oil field is moving forward, and we are now in the 
process of testing and monitoring across the project area (a number of 
prehistoric sites in the project area also require testing). Disturbance to 
the site with the metal piece is minimal. The oil company has made a great 
deal of effort to be as minimally damaging as possible to the area as a 
whole, including using previously established roads rather than blading new 
ones. The metal piece happens to lie next to one of these roads in a small 
narrow valley. There isn't anywhere else to put a road through that area 
without affecting other resources (including some NTU-related foundations 
and a building) and causing a great deal more disturbance. The original 
intention was to avoid the piece altogether and leave it in place as part of 
the historic mining landscape. It has become apparent, however, with the 
movement of the oil traffic and all of the rain that California has been 
getting recently, that avoidance may end very abruptly if a truck slides in 
the mud. Protective fencing won't help very much in that case. So, we are 
trying to assess alternatives.

Again, thank you for all of the suggestions and conversation. It is very 
helpful.

best,
Marcy