Charles Ellicott Commentary Psalms 78:16

"He brought streams also out of the rock, And caused waters to run down like rivers." — Psalms 78:16 (ASV)

Rock. —Rather, cliff—sela, the word always used of the event that took place at Kadesh (Numbers 20:8–11), as tsûr is of the rock in Horeb. The plural of this latter word in Psalms 78:15 is poetical and general.