I'm considering a tapered retaining wall - L shaped. The 90 degree would be the highest point of approx 30" inches. The long side is about 50 feet long and the short end about 10 feet long. I plan to fill in the area and make it level for a slab that will wrap around an in-ground pool. I plan on doing cutbacks or deadman ties aaprox every 8 feet.

How long would this last? 40 years? I realize water run off plays a roll. I was going to fill with crushed concrete. The slab would be about 10 feet wide also L-shaped. Price is my concern so I selected pressure treated. Is that the best choice? The wall does not have to look pretty but functional. A foot would be very expensive for cinder blocks.

Any suggestions?

I'm not a contractor, but I did a lot of research on this for my own walls.
You might consider interlocking blocks such as Anchor Blocks. They can be supported with geotextile fabric for higher walls or greater stability.

According to their literature, you do not need a footer, but only a bed of sand or crushed rock, and build part of the first course is below grade.

All the information is available on the web; however, I hope a more knowledgeable source reads your note.

I was very happy with the walls I made, 4' high and 15 to 30" long, tapered.

Good luck.

The lifetime for presure-treat really depends on things like water in the ground, exposure to weather, etc. I used pressure-treat a6x6 RR ties around a patio, and much of it pretty much rotted after 15 years. The portion that is above ground survived much better. Also, if you cut any of the pressure-treat wood you leave exposed surfaces that are not as well protected - they will rot first. I ended up replacing the wood ties with pre-cast blocks, and they work much better and (in my opinion) look better too. One final note - be sure that the concrete slab does not come in contact with the wood - the lye in the concrete mix can destroy the wood in a matter of a few years.