The star formation history of the northern and southern M31 disk is measured using samples of BV photometry for 4 ’ \times 4 ’ regions taken from the KPNO/CTIO Local Group Survey ( ) .
The distances , mean reddening values , and age distributions of the stars in these regions were measured using the routines of Dolphin ( 1997 , 2002 ) .
Independent measurements of overlapping fields show that the results are stable for most samples .
A slight distance gradient is seen across the major axis of the southern disk , and a mean distance of 24.47 \pm 0.03 is found by combining the results .
Higher mean reddening values follow the spiral structure .
The stellar age distributions are consistent with episodic star formation confined mainly to the gas-rich arm regions .
If these episodes were caused by propagating density waves , the waves did not cause significant star formation episodes in the gas-poor interarm regions .
Combination of all of the results provides the total star formation rate for 1.4 deg ^ { 2 } of the M31 disk for six epochs .
These results suggest that star formation in the disk declined by \sim 50 % from \sim 250 to \sim 50 Myr ago .
The lowest star formation rate occurred \sim 25 Myr ago followed by a \sim 20 % increase to the present .
The mean star formation rate for this large portion of M31 over the past 60 Myr is 0.63 \pm 0.07 M _ { \odot } yr ^ { -1 } , suggesting a total mean rate for the disk of \sim 1 M _ { \odot } yr ^ { -1 } .