Here are the latest and greatest gravity models that work best and my
methods section.  Any comments are welcome.  Enjoy! :)
Methods

A LaCoste-Romberg (L&R) model G gravimeter was used for all gravity
measurements. A total of 24 gravity measurements were taken in an
east-west profile across Warm Springs Valley, 21 were used for modeling.
A total of six measurements were taken in a N30W profile across Hungry
Valley, six were taken in an east-west profile in Red Rock Valley and
four in Long Valley. A total of 25 measurements were taken throughout
Virginia City. Warm Springs Valley data will be compared to the 1967
data collected by the Nevada Bureau of Mines. Eight of the Virginia City
data points will be used to determine an estimate of the sediment
density using the Nettleton method. The remaining seventeen points will
be used to create a Bouguer anomaly map.

Vertical control for all measurements was provided by a geodetic quality
GPS. Tidal variations and instrument related drift was corrected for by
regular re-occupation of local base stations. Hammer zone terrain
corrections B and C (1 meter to 54 meters) were estimated by eye in the
field. Bouguer earth density of 2.67 g/cm3 and a density contrast of -.5
g/cm3 was used in the reduction of all data. Regional anomaly effects
were corrected for by a simple linear approximation.

Initial basin depths were estimated using a Bouguer slab approximation.
This method gives a minimum depth to bedrock. However, the infinite slab
approximation works best when the lateral extent is much greater than
the depth of the basin (Abbott and Louie 2000). All basin depths were
calculated by three methods, Talwani inversion, infinite slab
approximation and by GM-SYS, a forward modeling program developed by
Northwest Geophysical Associates. Cross-sectional models followed the
transects of the gravity stations as closely as possible. All models
were created using GM-SYS.=20

The LaCoste and Romberg gravity measurement errors are estimated to be
1.17 g/cm3 for Warm Springs Valley, .18 g/cm3 for Long Valley, Red Rock
Valley and Hungry Valley and .21 g/cm3 for Virginia City. The transect
in Virginia City to be used for near surface density calculations had an
error of .08 mGal. Battery problems account for the larger error in the
Warm Springs Valley data. Much of the error from all the valleys is due
to more than one gravimeter operator in any data set. Elevation
measurements are accurate to within .15- .20 meters introducing a ~
.04 mGal error. Terrain corrections estimated in the field occasionally
approached .2 mGal. A 25-30% error is possible for the estimated terrain
corrections, producing a possible error of ~ .06 mGal. The total
estimated anomaly error is 1.35 mGal for Warm Springs Valley, .29 mGal
for Hungry Valley, Red Rock Valley and Long Valley, and .32 mGal for
Virginia City. The transect for near surface density contains less
elevation error. The elevation is estimated to be within .05-.10 meters.
The over all error for this data is estimated to be ~ .14 mGal.

The largest source of error in our results comes from our estimation of
rock densities and lateral variations. The lack of any density data of
the basin fill introduces significantly large error. The basement rock
has a significant lateral variation from 2.70 on the west to 2.38 on the
east (Gimlett 1964). It is possible that the depth error may be as high
as 50%.