backside of the desert -- [back of the wilderness, ASV; west side of the wilderness, ESV. NASB; far side of the desert, NIV]
H310, behind, after, -- ÇàÇçø
’ahar: A preposition meaning behind, after, afterwards. The usage is quite uniform, varying slightly according to context. Used more adverbally, it can mean such things as behind someone or something (Genesis 22:13); afterwards or after that (an event) (Genesis 18:5). Used more specifically as a preposition, it means behind (Genesis 37:17);
The backside of the desert, -- i.e. “behind” or “beyond the desert,” across the strip of sandy plain which separates the coast of the Elanitic Gulf from the mountains, to the grassy regions beyond.
He came to the mountain of God, even Horeb. -- Rather, “the mountain of God, Horeb-way,” or “towards Horeb.” By “the mountain of God” Sinai seems to be meant. It may be so named either by anticipation (as “the land of Rameses in Gen. 47:11), or because there was already a sanctuary there is the true God, whom Reuel and Jethro worshipped (ch. 18:12). - FSB
behind -- (i.e. to the west of) the wilderness] where there was good pasture. We do not know exactly where the ‘wilderness’ mentioned was. -- CBSC