April 24, 1970
Mr. Max Goodman, Geologist
Soil Conservation Service
P. O. Box 661
New Albany, Mississippi 38652
Dear Max:
Herewith are the copies, promised you some time ago, of available data on old sedimentation ranges on Big Spring Creek and tributaries, Marshall County, Mississippi. These data are from SCS work as part of the USDA Little Tallahatchie "Flood Survey" of 1939.
The map has been reduced from tracing made from contact prints of airphotos in 1939. It is not precise overall, but local details should be identifiable on newer airphotos, and generally with the topographic quadrangle maps (which were not available in 1939).
Descriptions of range end monuments (4" bronze plates, set in concrete about 6" high) have been copied from microfilm, which is partly illegible. The film is part of old SCS Stream and Valley Research Section files, which have been transferred from Washington to Fort Worth, now in custody of Graham Renfro at Fort Worth Regional Office (from whom I have borrowed them). Some details have been omitted because I can't read them at all. Others are very doubtful, as indicated by question marks and parentheses. Most others are fairly certain, but our experience (in other valleys) indicates that any particular number or word may be erroneous, although the errors are so few that we've been able to find almost all the monuments for which reasonable search has been made.
We have found two frequent kinds of discrepancies in the descriptions: (1) Distances to witness points were occasionally listed to fraction of a foot, but the decimal points are rarely legible, hence some may have been omitted in copying; (2) The range bearings were written, originally in such way that they are particularly difficult to read, and hence must be used with caution. Apparently they were usually recorded as magnetic bearings, but the descriptions do not specifically say so, and in a few cases appear to have been converted to true bearings. In most cases we have found that the line can be closely approximated by assuming the recorded 1939 bearing to be from magnetic north, and adding 1°20' to the azimuth as correction for shift in magnetic declination since 1939.
The original notebooks are missing, presumably in or discarded from Forest Service files. The cross sections, with depths of modern sediment from 1939 borings, have been replotted from the worksheet sections, plotted in 1939 for planimetry. For some other valleys there are copies of survey notes on microfilm, from which the plotted sections can be checked; in those cases small plotting errors were found to be common, but never enough to introduce serious errors in average elevations for a range. Presumably similar, unchecked plotting errors may be present in the work sheets for Big Spiring, and if so have been copied into our new drawings. The range monument descriptions, on microfilm, do not include elevations. Hence elevations, as shown on the sections, are known only to nearest tenth of a foot. Apparently elevations plotted at zero, and at the opposite end of each section, are on the monuments, for profile notes of some other ranges are preserved on microfilm, and do not show ground shots taken at the end markers. But this is one question of slight uncertainty requiring consideration in any resurveys.
All of the Big Spring ranges are plotted on arbitrary, assumed datum, so that loss of both monuments would make resurvey impossible. For some other valleys, ties were subsequently made to sea level datum. If the notebooks are ever recovered, it may thus be possible to determine more adequate vertical control.
The old 1939 boring notes are completely recorded on microfilm, and are legible. However, I've not yet checked those for Big Spring against the plotted sections. Elsewhere I've found them almost always in agreement, but in a few places the old soil has been erroneously plotted a half foot or foot too high or too low. In many places the boring notes do not convince me that the old soil was correctly identified, but that is partly because of difficulties in describing gradational changes. In some places I would be more conservative in judging the thickness of modern sediment; but judgment of the man who saw the samples should be more reliable. The changes I would make would not materially alter general conclusions. My principal questions concern places where no dark buried topsoil was identified, but old subsoil was identified from concretions and lighter colors. It appears the old subsoil may have been accepted as base of modern sediment, even where some old topsoil was perhaps present but not distinguished in the sample descriptions.
I've not yet found opportunity to search for any of the Big Spring range markers, and it appears unlikely that I can make resurveys there in the near future. If you find it possible to do so, I shall be much interested in hearing of your results.
Sincerely,
Stafford C. Happ
Res. Geologist
Encls.: Map of sedimentation ranges, Big Spring Creek;
Description of range end monuments;
Cross sections showing modern sediment as of 1939 (in 2 sheets).