It definitely is a yucca rostrata and definitely not a dragon tree. The yucca r's top flower stalk should produce a plume of white to fleshy colored flowers upon blooming. That type of plume would be the definitive identification for this type of yucca. In fact upon looking closely at the flowering stalk in your pictures I can see that coloring emerging in the flower buds.

thanks for that info....can you tell me how often it flowers and what happens after it has...do I need to cut that flower head off?

A mature plant will flower in spring, which is now the case where you live, on a yearly basis. Once flowering is finished, the apical flower plume stem will fall off on it's own. This leaves an open wound which is nothing to worry about going into a hot dry late spring and summer as a callous will form over it. The only cause for concern would be if you had a period of wet weather while the wound was still open(callous completion takes about a month). The moisture on the wound could initiate a fungal rot which would eventually kill the plant. The remedy would be to get up to the top and cover the wound with a glob of cement or tree wound salve before the inclement weather starts. Looking at the location of this yucca do not attempt this as there is a possibility of injury to yourself or another either trying to get up to the top or down from it.
I might add that you should not ever water this plant. The leaves of the yucca have water storage cells in them which serves as it's water reserve in the dry season.

Thanks so much for all that invaluable info...we purchased this property nearly 4 years ago and it has not flowered until now - so much energy must go into the flower plume...amazing plants.

PS should I cut off the dead leaves at the bottom of the plant to expose the trunk??

Kindest regards - Jude.

I forgot to mention that after flowering, berries are produced within which one will find yucca seeds. You can harvest these once the flwr stem falls off. Seed germination reliability is 80 %, but this plant is a slow grower. The plant I see in your picture is probably 25yrs -30 yrs old. Some do cut off the dead leaves, but that is an esthetic choice. I prefer this plant to be in it's natural state of appearance. Once the leaves are off the trunk looks rather thin and it reminds me of a groomer who cut the hair of my Pomeranians down to close to the body, kinda spindly.

Blimey Eclectic,you're some authority on yuccas! Almost wrote a book there! Most impressive..

Don't know what this is but it is a magnificent specimen. Well done!