Practice. Practice. Practice.
Create a down hill corner that is on soft and flat with maybe a bit of a berm on the outside. Could be on grass or soft dirt terrain. Fill your corner with sand or mud. Not so much as to slow you down, but to make it a bit slippery. Wear lots of padding. Put out cones, flags or something you can use as braking points. Brake before you turn. Thats 1 thing less to worry about. Guide your bike thru the turn with your body. As you lean, your arms will naturally counter steer the front so there is no need to actually turn the handle bars. Look thru the turn as mentioned above. Brake later and later each time and carry more speed until you fall. A low side fall will probably not hurt on grass or mud.
The fear of falling can be overcome once you have hit the deck a few times. Fast people prob canāt count how many times they have fallen.
Sliding wheels thru a turn will become more natural the more you do it.
I have a different opinion on this. You donāt need to fall to learn. If you normalize falling, you set yourself up for injuries. The guidance I give to my kids is the primary goal when riding is to ride in control, pick good lines, and not fall. Skills will build slowly but surely.
Iāve never crashed on either my road bike or gravel bike. And Iāve had only 4-5 risky crashes on my MTB in over 10 years of riding. Crashing is bad news, especially when you are older. Look at what happened to Nate with concussions. I think he tried to push himself too quickly up the learning curve. Eg I recall him saying he was trying to follow a wheel closely of a rider on Porcupine Rim to get used to a race situation. Thatās not the trail to follow an unknown riderās wheel when you are learning to ride MTB. Not the best decision.
I agree with this, just donāt plan on it being OK to crash 
I hear what you are saying in a very controlled āsoft landingā situation, but I think there are other ways to get there. Maybe itās an age thing (in my mid 50ās now), but hitting the deck isnāt part of any progression Iād recommend for most folks. Lots of good tips in the thread, Iād just add that building confidence and skills slowly is the way Iād recommend. Iāll still take some chances on descents in big races, but nothing that gets me out of my comfort zone. Iāll also echo the importance of bike choice. I used to race gravel on a size 56 trek domane (which is a relatively stable platform for a road bike) and there were situations where it was terrifying on fast technical descents (I still have nightmares from BWR cedar city). Have since switched to a 58 Checkpoint and itās so much more confidence inspiring (ie faster) when things get heated. Iāve beat this drum here before, but I personally see very little upside to āfast handlingā gravel bikes from a performance/speed standpoint. The crux is probably one of the best bikes out there if you are looking for a single bike to do it all, but for gravel racing Iād rather have something as stable as possible for courses with fast technical terrain.
Or better yet, study the route beforehand. Please do not look at your bike computer while on a descent! Or while racing close to other riders. Itās critical to look ahead. Looking down at the front tire, computer, whatever is part of the problem of not being able to descend faster. (Also a good way to miss potholes, ruts, sand, etc.) The further you look ahead the faster you will go. Itās a Jedi mind trick.
Watch some DH mtb world cups or EWS. Look at their body position and where their eyes are looking. Or watch Tom Pidcock 
Emulate. Practice. Enjoy!
Mostly agree if you are on technical terrain, but having the map up can help in certain situations. There is a fast fire road descent at Leadville and I always use the map page to get a feel for the turns coming up. Some are 180ās (require serious braking) and some are sweeping (maintain 40+mph). All on loose over hard surface. Itās a 20+ minute descent with too many turns to memorize (for me anyway). The surface is pretty good, so a quick look at the map is reasonably safe. Iād argue itās a good safety tradeoff to make sure you arenāt flying into the hairpins too hot.
I donāt mean to discount your Leadville experience and what worked for you there.
Just, in the context of the original post it might not be the best approach:
Using your eyes is the first thing that any good skills coach is going to teach. The second thing they will teach is body position on the bike. Those are the 2 fundamentals that help me more than anything in riding down steep hills. I say this from a background of having had a few bone-breaking crashes and invested in a lot of skills coaching. (Too long of a post that oneā¦)
Loose terrain is scary to me too! Especially this time of year in the dry CA summers. We have some ridiculously steep trails nearby where I live and I just donāt ride them when itās dry and loose. I feel safer on grippy granite rock rolls, TBH! The best tips I have for loose stuff:
a) Brake and scrub speed before you hit the loose sections. This requires your eyes (again) to be up and looking forward at the texture of the road surface way ahead of you and planning safe spots for braking. If you see a grippier patch ahead, plan to scrub speed there so that at no point are you riding out of control.
b) Trusting that as long as your tires have contact with the ground and are moving, you will have traction.
c) Iād recommend the course on cornering in ryan leech connection. for breaking down skills into bite-sized chunks and showing videos on how to do them. Mtb skills and āgravelā skills overlap quite a bit.
Iād be interested in othersā experience of mastering riding marbles on gravel bikes!
This is criticalā¦.and goes along with the idea that speed / momentum can be your friend is loose areas. If you brake is loose stuff, it reduces your traction and tries to move you off your chosen line (to the outside).
But this also is very counterintuitive (and scary!). You need to build the confidence / skills by slowly pushing the edges of your capabilities / skillsā¦ā¦but it all starts with looking up and ahead.
10%+ is some serious downhill grade and on a loose gravel road that you donāt know. It should be a bit scary!
Personally, I was an above average downhiller on a road bike back when I raced. Iād always leave team mates in the dust on a twisty descent. On mountain/gravel I could care less to take risks. Iām not at the pointy end of a race and could care less to push the envelope off road.
There are mountain biker types that say that if you donāt fall off once per ride, you arenāt pushing it enough. My take is that if you fall off more than once per year then you are doing something wrong!
Now, if you are racing then itās another story. As others have said, you just have to practice. You are also going to be at a huge disadvantage to locals who have been down the descent 100 times. There little way around that other than riding the course many times and that is usually not possible with longer gravel events.
Yeah, I hate when people say that. Itās not helpful to be terrified and just barely make it down something or crash on it. It sets you back, actually. You want to work up to things so that you are relaxed and confident. Sometimes crashes are pretty benign and other times youāre off the bike for a month or two or three. 
It takes time to come back from that mentally too. You just end up missing out on some great riding and training.
Lots of good tips in here. I wonāt add to them but I will put out a PSA.
Be careful of gusting crosswinds when youāre on loose gravel!
Story: I was coming down a steep (about 12%) straight-line gravel road that had a complete layer of loose gravel covering the hardpack. Since it was straight for about 1km to a corner (which I could see), I let it open up to 45-50km/hr (which was pretty challenging on the loose gravel) and was riding in the centre of the road. A massive wind gust blew sideways and took me left. The road was also sloping down to the left. Iām an avid mountain biker with pretty good bike handling, but there was absolutely no way I could stop drifting. I was being blown sideways while āgravel surfingā downhill (horizontally).
There were no features on the road where I could find traction. Fortunately for me, at the edge of the road there was about a 4in wide berm-like ridge that let me turn back and save it. If I didnāt get the turn in on that ridge I was going to crashing hard into uneven bumpy rocky ground.
I had the same hard leaning curve, when I moved from N Texas to Oregon.
Thereās lots of good advice above, but most of it will take time and practice to take effect.
Hereās how you can cheat.
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Donāt get overwhelmed with all this advice. Pick one thing, like ālook aheadā, and repeat it like a mantra until itās automatic. Practice it on your normal N Texas rides, even if you sent think you donāt need it. Then focus on another skill.
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Get. A. Dropper. Descend seat down in the drops; never in the hoods. We obsess over a mm here & there in geometry; this could lower your center of mass by 3-5 inches! It feels like cheating.
People love to say you donāt need a dropper on a gravel bike, but it was a game changer for me. On my last gravel bike with a rigid post, I felt like I could easily fly over the bars on steep descents.
My current gravel bike has a longer wheelbase, big tires and a dropper post. I think I hit 45 mph on my last gravel ride but felt much more confident with the dropper. Itās still scary though and I donāt like going that fast if I can avoid it without riding my brakes 
I think it depends on how tall you are, and bike setup. Iām 5ā9ā, and my saddle is about level with the tops of my bars. I donāt have a dropper on my gravel bike and feel perfectly fine on descents.
If I was taller and/or had a big saddle-to-bar drop, I think a dropper for sure would be helpful.
One consideration with a dropper post is they donāt flex. So if you currently have a Seatpost that flexes, a dropper may feel more uncomfortable.
Great points! I know youāre comfortable on a MTB (Iām not 
) so I bet having those skills helps a bunch too.
Iām 6ā5" and have ~10 cm saddle to bar drop on my gravel bike, so a dropper suits me perfectly.
Yeah, 10cm is a lot. I can see a dropper totally helping.
MTB skills and familiarity really help on road and gravel descents. Thereās nothing intimidating about a road or gravel descent when youāre used to riding technical MTB trails. And you get comfortable with bike-body separation, leaning the bike, letting the bike go a bit squirrelly (on gravel), etc.
Iāve had a rigid Karate Monkey for years and Iāve just recently put a new fork on it and started riding some local trails with it. Hopefully thatāll help over time.