Is this single or something else?

[Urfunny464]

My mom gave me an incomplete work she found at Goodwill. I recognize 10 rows of hdc, but in-between is something else. What stitch is this? I notice the yarn doesn't twist at an angle on those 6 rows in-between, the yarn seems to stitch across. I can insert a photo if allowed but don't see where to do so. So here it is: https://photos.app.goo.gl/oNdmD2Ni27NPwyWX8

[Granny Square]

I think your photo is upside down from the way it is made, I flipped it over.  This was made in turned rows or rounds.  At first I thought every so often a row was made in the back loop only for the ridges you marked with slashes / / /, but  I don't that's 'it' tho, because while what I described makes a ridge, it's straighter across, and there would be 1 ridge per stitch, and I'm seeing 2.  Hmmm....

[Granny Square]

This link shows SC BLO--which if it comprises all the (turned) rows, makes ribbing.  If made in a spiral, say on a hat, would make a raised spiral.

[bgs]

 

Black arrows pointing to hdc

You can see it here.

https://www.thesprucecrafts.com/how-to-half-double-crochet-stitch-3576850

 

Not sure maybe alternates 2 rows hdc, 3 rows sc, 2 rows hdc