I am wondering what causes the terraced lines on grassy hillsides.
These are narrow, regularly spaced "tracks" that cover the hill. They
look almost like map contour lines. (I wish I could find a photo of
the phenomenon. I have seen it many times on hillsides throughout
California and the Pacific Northwest.) They look like animal paths,
but I am dubious that animals would behave in this fashion, i.e. walk
all over the hill rather than following one or two well-worn paths.
Are these lines formed by animals, and if so, which ones? Or if they
aer formed by a geologic process, what is happening?

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Request for Question Clarification by tutuzdad-ga on 29 May 2003 16:59 PDT

Are these lines verticle? It would be difficult (if not impossible) to
speculate about the cause of this without a photo.

Regards;
tutuzdad-ga

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Clarification of Question by stellamaris-ga on 29 May 2003 17:26 PDT

The lines are horizonal. I wonder whether redhoss (or some other
reader) has a digital camera and could take a picture of the
phenomenon.

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Request for Question Clarification by pinkfreud-ga on 29 May 2003 17:48 PDT

If the lines look like the ones in this photo, I can tell you what
they are, and what purpose they serve:

http://www.mortalwombat.com/Special/Hillside.jpg

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Clarification of Question by stellamaris-ga on 29 May 2003 18:10 PDT

Good try, but no. Those lines are wider than the ones I'm talking
about, plus they are obviously a surface phenomenon (they look like
the grass has been mowed in different directions rather than being
formed from the earth itself). The ones I've seen make a visible
stairstep pattern when viewed in profile.

Hi there,

As someone who grew up on New Zealand farms, I instantly knew what you
were describing. They are sheep trails. In French they are known as
"drailles" (ways of the ewes).

Why sheep? Well, more often than not, when relaxed, they follow each
other in single file. Especially on the side of a hill. So if you have
100 sheep following the same path, a trail might begin to form,
especially if it is wet. Once a trail is there, it is easier to walk
on than other parts of the hillside.


Here's a good photo:
http://www.lukepowell.com/palestinehills/P2.HTM

This isn't so good:
http://www.agritech.org.nz/products.htm

A photo of a singular trail:
http://eap.ucop.edu/eap/photos/contest/uk_i/uk-hm1.htm

You can just make out the terrace effect in these pics:
http://www.seafriends.org.nz/enviro/soil/f982420t.jpg
http://www.gdc.govt.nz/cons/soilcon/soilcon4.jpg

And some sheep following each other:
http://www.kikitours.co.nz/index-main.jpg


Some mentions I found online
----------------------------

Apparantly "sheep tracks are never straight as sheep continually turn
to watch behind them".
http://www.lifestylefarmer.com/articles/019e_sheep_senses.htm

"Trail: Little used, but not too difficult to follow. Numerous sheep
trails in the area can cause some confusion."
http://www.utahtrails.com/RowBench.html

"You can bypass the top of the chute by following narrow sheep trails,
more or less horizontally (westward), across the slope towards the
lowest point on the saddle."
http://users.lvcm.com/jlboone/Lake_Mead_Area/N-Shore_Pk_W/N-Shore_Pk_W.htm

"Sheep trails are formed perpendicular to hills and around the hills."
http://216.239.57.100/search?q=cache:TSC_AViWDO4J:www.ttsfo.com/Gunnison/FG-Minutes-5-23-02.pdf+%22sheep+trails%22&hl=en&ie=UTF-8

"...viewed sheep and goats, and traversed ancient sheep trails that
cut across scree ridges as the winds whispered in our ears."
http://adventurepages.com/GtxPg.asp?rq=Pg&GtxId=2436

"... sheep-trails criss-cross the steep slopes on which you can
sometimes see the animals sunning themselves."
http://www.wtc.ab.ca/tedyck/GuideBk.htm

"The rambler can use the " drailles " (the name given to narrow tracks
that were originally used mainly in the transhumance of animal.)"
http://www.les-vans.com/English/loisirs.htm

"The hill is covered in a myriad of faint paths, mostly
sheep-trails..."
http://www.b-mercer.demon.co.uk/whang.htm

"There is some noticeable terracing by sheep trails ..."
http://216.239.39.100/search?q=cache:yw-NLw9TgpQJ:ag.utah.gov/mktcons/rangeland/pdf_files/1997v2/97wmu19b/wmu19b-11.pdf+%22sheep+trails%22&hl=en&ie=UTF-8


Search Strategy
---------------

Most of the photos came from doing a Google Image for "sheep", and
restricting it to .nz sites.

Most of the quotes came from Google searching for "sheep trails".


Best wishes,
robertskelton-ga

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Clarification of Answer by robertskelton-ga on 29 May 2003 21:57 PDT

Here's another picture, although they have attributed the trails to cattle:
http://www.sharnoffphotos.com/environment3.html

Excellent answer, and many useful links. Thank you so much!

Hi stellamaris,
     I live outside Riggins, Idaho in a river canyon. Directly across
from my front door is a very steep hillside which has the "terraced
lines" you refer to (there are deer grazing this hillside every day).
I have wondered myself how they are made and have asked several
oldtimers. I hope that someone answers your question with a definitive
answer because I have not been convinced with the answers I have
gotten. However, I have seen some very pronounced terraces on slopes
where domestic sheep have been grazed for years. I think that the
terraces are at least started by grazing animals (domestic or wild)
and then possibly accentuated by mother nature. This is only an
opinion formed from personal observation.

Robert Skelton is right. The tracks are made when grazing animals walk
along a hill side while grazing. To spend as little energy as
possible, they graze along height contours. After a while a terrace is
formed and they prefer this as a track. Under influence of their
weight, and by compaction, the track becomes a stable feature. Cattle
form such tracks more quickly because of their weight, but cattle are
not usually grazed on steep hillsides. Not everywhere do these tracks
form. It is usually an indication of good (soft) top soil on a stable
hill face, and more so when facing away from the sun. The terraces
help against soil erosion, retaining more moisture and slowing rain
water down. So grazers have a stabilising influence on their
ecosystem. Look at this photo showing sheep grazing tracks in the
setting sun in northern New Zealand.
http://www.seafriends.org.nz/enviro/soil/sheeptracks.jpg