Mansfield Creek's watershed covers 143 km2 (55 sq mi),[6] and its mean annual discharge is estimated at 1.46 m3/s (52 cu ft/s).

[6] The mouth of Mansfield Creek is located about 45 km (28 mi) northeast of Telegraph Creek, British Columbia, about 50 km (31 mi) west-southwest of Dease Lake, British Columbia, and about 210 km (130 mi) east of Juneau, Alaska.

[8][9] Mansfield Creek originates on the south flank of the massive Level Mountain shield volcano, about 27 km (17 mi) southeast of Meszah Peak, the highest peak of the Level Mountain Range, a cluster of bare peaks on the summit of Level Mountain.

From its source near the large U-shaped valley through which Beatty Creek runs, Mansfield Creek flows generally south then east through wetlands, lakes, and barren lands atop Level Mountain's high lava plateau.

From this high plateau Mansfield Creek enters a steep forested canyon carved into the escarpment on Level Mountain's southeastern edge, through which the creek flows east to empty into the Little Tuya River.