Over time dust from the air and organic matter fill in the spaces between the rocks/stones often used as decorative something in place of plantings and the only really effective means of getting rid of that, and preventing unwanted plant growth there, is to remove those rocks/stones and clean out the accumulated soil those unwanted plants grow in.
Spraying growing unwanted plants with something that kills them simply adds more organic matter to that mix that accumulates in the spaces between the rocks/stones which provides more opportunity for more unwanted plant growth.

You could use one of those blow-torch things to burn the dry grass, just keep a hose handy. They sell the blow-torch thingies at Harbor Freight....can't remember now what they are called but are designed for landscape use.

Those flame weeders have been the source of more brush and grass fires than many a rural firefighter cares to count. Unless used with great care they are dangerous and also use a non renewable resource as the fuel.

Flame weeders are very effective, and low cost, low labor solutions for this kind of situation. Red Dragon makes a good one, available on Amazon and other places. kimmsr is right that you do need to be careful not to start unwanted fires, but in our dry environment, this is the tool of choice for eliminating dead or live weeds in rock. It takes only minutes to do a garden bed, and the weeder will leave a clean looking surface that can be touched up easily with the weeder again as needed. I've seen these devices used on acre size lots full of weeds to great effect. If you have a weeder, you won't need to buy herbicide, and weeder will pay for itself quickly. Probably the greatest benefit I see is the labor: it would take me hours to weed even a relatively small area by hand, and I would need to be doing it again soon. The amount of propane needed is quite small, and easily compensated by the hours of your time saved. As noted above, soil gets into the rocks over time, and you would need to move and clean the rocks to even start to keep more from growing in the area. However, even this huge effort would be defeated over time as new soil and debris comes onto the rocks. The weeder helps to eliminate that debris.
Renais

Thank you everyone!

I had tried the flame idea on a small scale and while it quickly and easily burned the majority of the material away it left the ground and rocks with a scorched appearance that is proving hard to eliminate and also left the base of the grass charred but still present. I would note that in my case the weeds are isolated in rocks in an enclosed back yard and are far enough from structures or other potentially flammable materials that I was not extremely worried about starting an unintended fire. Plus, I had my hose on stand by and ready to go.

I am thinking that I just need to stay on them with the manual labor approach, getting as much sun and air on the remnants as possible and just hope the materials breaks down quickly.

Was told to use bleach water then distilled water or vinger then baking soda