  We have investigated the possibility that large rock salt formations might be
suitable as target masses for detection of neutrinos of energies about 10 PeV
and above. In neutrino interactions at these energies, the secondary
electromagnetic cascade produces a coherent radio pulse well above ambient
thermal noise via the Askaryan effect. We describe measurements of
radio-frequency attenuation lengths and ambient thermal noise in two salt
formations. Measurements in the Waste Isolation Pilot Plant (WIPP), located in
an evaporite salt bed in Carlsbad, NM yielded short attenuation lengths, 3-7 m
over 150-300 MHz. However, measurements at United Salt's Hockley mine, located
in a salt dome near Houston, Texas yielded attenuation lengths in excess of 250
m at similar frequencies. We have also analyzed early ground-penetrating radar
data at Hockley mine and have found additional evidence for attenuation lengths
in excess of several hundred meters at 440 MHz. We conclude that salt domes,
which may individually contain several hundred cubic kilometer water-equivalent
mass, provide attractive sites for next-generation high-energy neutrino
detectors.
