We report the measurement, at 0.51 K and up to 28 T, of the magnetoresistance and Hall resistance of a dilute two-dimensional electron system with 6×1010 cm-2 carriers in a GaAs-GaAlAs heterojunction. The existence of an anomalous quantized Hall effect for a fractional Landau-level filling factor of 13 was confirmed. The magnetoresistance showed a substantial deviation from linearity above 18 T and exhibited no additional features for filling factors below 15 down to 111. The results suggest that a transition from a quantum liquid to a crystalline state may take place. © 1983 The American Physical Society.