Print this pageThe Megabreccia Reservoir at 
Ghost
Ranch Oilfield, Railroad Valley, Nevada
The reservoir at Ghost Ranch is a large catastrophic Neogene rockfall deposit, known
as a sturzstrom. The Ghost Ranch sturzstrom
is a limestone and dolomite breccia, which
predominantly originated from Paleozoic carbonates. At the 58-35 dry hole east
of the field, Tertiary valley fill sediments were encountered below the breccia, which confirmed that the reservoir is a late
Tertiary landslide. The brecciated nature of the
reservoir is clearly expressed on an imaging log. The intense fracturing
imparts huge permeabilities implied by production
tests (4320 barrels of water per day at the 58-35). The top of this deposit is
a prominent seismic reflection that extends southward to Kate Spring field,
interpreted by French, 1991, to be a landslide deposit. Because of the continuity
of the seismic reflection, the Kate Spring reservoir is interpreted to be the
same lithostratgraphic unit as the megabreccia at Ghost Ranch. The deposit covers
approximately 1500 acres and the volume of the deposit is estimated at 0.3
cubic kilometers (380 million cubic yards). According to relationships derived
for modern sturzstroms of this size, it is estimated
that the Ghost
Ranch rockfall had a runout of 8 kilometers (26,250 feet) and a drop height of
1.2 kilometers (4000 feet). This drop height is very similar to the present day
relief from the Grant Range to the valley floor. Foliations within the arched
core complex of the Grant Range dip into Railroad Valley and may have increased
the tendency for such a large landslide to occur.