Thank you to all participants.

AndieKae gave the only correct answer.  Her reasoning and mine are as follows.

The piece contains all and only the pitches of the C key signature, that is, exactly the seven natural pitches: C D E F G A B.  So the key signature is C.

The tonic (see http://en.wikipedia.org/wiki/T.....28music%29)  of the piece is D.  This is because each phrase and the piece itself end on D.  For this piece, there is a sense of resolution or stability when reaching D.

It follows that the scale is D-Dorian.  Here is why:

First think of ascending the major scale of the key signature, in this case think of ascending the C-Major scale, since the key signature is C.

Each note in a scale represents a scale degree (see http://en.wikipedia.org/wiki/S.....ale_degree).  The mode is determined by counting the scale degrees in ascending the major scale from the name of the key signature to the name of the tonic. 

If the key signature and the tonic were the same, the piece would be in major mode.  Since they are different, the piece must be in some other mode.

In general, the difference in scale degrees in going from the key signature to the tonic determines the mode as follows:

0: Ionian (Major)

1: Dorian

2: Phrygian

3: Lydian

4: Mixolydian

5: Aeolian (minor)

6: Locrian

In this example, there is a jump of 1 scale degree in going up the major scale from the name of the key signature C to the tonic D.  Therefore the mode is Dorian.  Both the name of the tonic and the name of the mode are used in the scale's name.  So the name of the scale is D-Dorian.

This comes from Dancing in the Meadow, on the 1976 album Wild Swans Against the Sun, by Michael Martin Murphey

I didn't find the original.  Here is a cover:

It is basically a banjo piece, but there might be ways to adapt it to a bluegrass band.

I feel that the lyrics are outstanding and may give life to this piece a hundred years from now.

http://www.metrolyrics.com/dan.....rphey.html

The original is more energetic than this cover.  It features John McEuen of the the Nitty Gritty Dirt Band, on fiddle and banjo.   MMM plays clawhammer banjo and guitar and does the lead vocal.  There is also mando, piano, lap slide steel, drums, and synthesizer.