Here's a better photo of the wrinkling:

Can you poke gently at the bottom area, is it squishy/mushy/gooey, it doesnt look like rot but you're growing it differently than how the nursery was growing it.

I did. It seems very slightly mushy where it's wrinkly and less so toward the bottom.

Your Oreocereus celsianus looks fine from here. I'm not sure I like the soil mix, but the plant looks pretty good. There is no way it gets "plenty of light" indoors. Look up the natural habitat of this plant. Water less this time of year to induce dormancy through winter. Some wrinkling is OK.

Brad

I don't know what you mean by wrinkly. I see new growth, which is a good thing. Water only when completely dry in the summer. Never water on a schedule. I don't water my cacti at all from November through February.

I think your cactus will be fine.

Christopher

It looks fine even with the top pointed like that?

Yeah, it was round at the top not even a week ago and then suddenly it started to become pointed which led me to suspect etiolation. But now, as you also have noticed, the top appears dark to me. I'm glad I got other opinions. The hair and spines are definitely covering the rot if there is any. I guess I won't know for sure until it's too late sadly. It's a shame, cause I really love this cactus.

I am not so sure about the soil you say is very well draining - from what I see in your photo, I don't think it is, but could be wrong. What kind of soil is it?

It's sand, soil, and small pebbles. Is there a specific potting soil you recommend? The water drains right out of the bottom hole on this one.

sand+soil = small particles(only difference would be is sand has large 'grains'-at least size that would not fall thru a mosquito screen or ordinary kitchen sieve)

pebbles = much larger than two above; doesn't help drainage at all since small sand and soil just fill any space between pebbles. Are these pebbles mixed with other two or? - I can see some on the surface but they don't add any drainage there (there are good to use for top-dressing this way thou)

If you see water draining thru the bottom, does it actually wet your substrate or does it just 'slide' around it?

So no pebbles in the sand is what you're saying? The ones in the surface were decoration. But I moved a lot to photo my (bad) soil.

I can run to the hardware store and make a new mix. I suppose this one just has different needs than my other desert cacti. Fault of mine for not paying attention to its normal habitat. So you're saying larger sand particles, potting soil and..?

The soil does get wet initially, but dries out within a day or two. Water does not linger when being watered but rather soaks right on through. But the potting mix does appear to get adequately wet. I could be wrong however...

Vanessa

From your description of mix it sounds that it does get properly moist - only you can judge that. Sand is usually very fine and typically decrease drainage rather than increase - it clogs up any spaces available between larger particles. But if it is coarse, it would work. And there are ppl that grow succulents in sand very successfully - but they have lots of knowledge and experience...

Grit in the mix is desirable ingredient; pebbles are usually too large (what's visible in your photo is too large for the mix, but good for top-dressing)

Grit should be about size of aquarium gravel, and any other additional materials too. Many of us use a gritty mix. There is very good and quite detailed info on this forum if you search for "gritty mix". There could be some adjustments made to it using suitable substrates - whole idea is to create well-draining and airy mix. Perlite, grit, scoria, turface, pumice are some that are used most often. Small bark is used too.

I use mix of grit (chicken grit), perlite and turface - these are quite easy for me to find. And I use top-dressing a lot, sometimes just chicken grit, sometimes pebbles and/or rocks - they help to anchor newly planted plant (and my hope is that they deter at least some digging by squirrels - just a little - since I keep plants outdoors).

Rina

Ahhh okay. Well, thank you so much for your help. Thanks to everyone. I have a horrible feeling that top is rotten, but I can't see it if it is and it's a shame honestly. I'll take your advice and refine my mix. I had a feeling perhaps my ingredients/portions were wrong, but like I said, I'm new to this. There's only so much you can read on the Internet. I can't seem to decide what to follow or not.

...follow ppl that grow them as a hobby/passion...like members of this forum. We want them healthy and grow for long time, and bloom, and reproduce...not just a short display, that will be replaced with a new purchase when it declines...:) Welcome to the club!