Hydrologic variation in the northern Great Plains during the last two millennia. 2000. Fritz, S.C.; Ito, E.; Yu, Z.C.; Laird, K.R.; Engstrom, D.R. Quaternary Research 53: 175-184.
Possible solar forcing of century-scale drought frequency in the northern Great Plains. 1999. Yu, Z.C.; Ito, E. Geology 27(3): 263-266.