PDS_VERSION_ID        = PDS3
RECORD_TYPE           = STREAM

OBJECT                = TEXT
  PUBLICATION_DATE    = 2009-11-15
  NOTE                = "Sample context description"
END_OBJECT            = TEXT
END

Seven-unit sequence of the Deschutes Formation, visible on a road cut along
the Crooked River. Unit designations are for the purposes of this study only.

Deschutes Formation Basalts:

Most of the hard, black basalt flows came from shield volcanoes east of
present-day Mount Jefferson at the eastern edge of the Cascades.  Other
basalts came from vents in central and eastern parts of the Deschutes Basin.  


Deschutes Formation Ignimbrites:

The abundant Deschutes Formation Ignimbrite strata are interspersed between
lava flows and sedimentary units.  These porous, silica rich ash units vary
greatly in texture, content, and consolidation. Most of the ignimbrites of the
Deschutes Basin have three parts:

1. A thinly laminated, poorly consolidated layer of ash or pumice at the base
of the ignimbrite formed by the initial contact of the rapidly moving cloud of
ash and gas with the cold ground. (The hot, laterally ejected cloud of ash and
gas hugs the ground and can travel at speeds up to 120 km/hr.)
2. A matrix-supported, poorly sorted pyroclastic conglomerate, usually with
pumice clasts.  This is the thickest portion of the ash flow unit.
3. A layer of ash fall deposits composed of the last of the ash cloud to
settle.  This forms the top of the ignimbrite unit. 

Deschutes Formation Sedimentary Deposits
  
Sedimentary deposits of the formation are poorly cemented, clast-supported
conglomerates and volcaniclastic sandstones, recording floods and braided
river channels.  Some deposits, with boulders as large as 12 m in diameter,
show evidence of sudden releases of debris from the Cascade volcanoes.  Other
deposits record turbulent floods of gravels and sand.