Dicot limb rolled into lahar McQueen Ranch Sweet Home OR polished petrified wood

Description

Undetermined dicot angiosperm wood (Incertae sedis)
Little Butte Formation, Mehama Volcanics unit, Oligocene
McQueen Ranch, Sweet Home area, Linn County, Oregon
A very unusual specimen with an interesting story to tell!  The McQueen Ranch was across the road from the former Marker Ranch (now called Holleywood Ranch) which produced some of the best preserved wood in the Linn County Petrified Forest.  This stick of dead and down wood was rolled into a thick blanket of volcanic lahar following the volcanic eruption of Mount Mehama.  Lahar is a word originally derived from the Indonesian language in Java and it means a flowing, usually violent, mass of material ejected from a volcanic vent which combines with water and whatever soil and vegetation is in the area to create a hot mudflow that becomes concentrated in rivers or smaller stream channels.  If they have sufficient gradient, they can be exceptionally destructive.  Imagine a hot, viscous mudflow with the consistency of wet concrete and you can get an image of what a lahar would look like.  The difference between a lahar and a flow consisting of only pyroclastic material shows up on this specimen.  The lahar picks up anything in its way - either destroying it or taking it along for the ride.  In our specimen, the stick of wood is being taken for a ride while the flow picks up small pebbles and bits of soil on its journey.  Notice in the photo that you can see just how angular all of those pebbles and bits are.  These small bits are definitely not river-tumbled with smooth surfaces.  This angularity is often some of the best evidence of a lahar flow.  The viscosity of the volcanic material in this particular flow made it possible to actually roll the stick into a larger cylinder before the entire mass cooled and was covered over by additional ash and mud.  It is not possible to determine the source of water that made the flowing mixture possible.  It could have been a heavy rainfall during the eruption, it could have been an existing stream, or it could have been a mass of snow which was immediately melted by the hot pyroclastic material.  Whatever it was, it did a fabulous job for the petrified wood collector in producing this exceptional specimen.
So, how do we know that the wood was "dead and down"?  The answer lies in the fact that the preservation of the wood reflects a lot of rot that had taken place before the wood was rolled into the lahar.  It obviously was not fresh growing wood.   It can be easily assumed that the volcanic ash had dropped considerably in temperature since the wood otherwise might have been incinerated rather than enveloped and preserved.  What a great, interesting story it tells.  This end cut measures 5" x 4.5" on the polished face and it varies in thickness up to .75 inch.
We specialize in petrified wood and plant fossils which are accurately identified as to locality of origin and family, genus or species. We don’t guess and when we don’t know, we say so! Your specimen will come with a label identifying the specimen, the locality where it was collected, the formation and age of the material and any other pertinent information we have gleaned from our literature search.
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