Rare is the prospect who starts out at first base and stays there forevermore.

It's a position that prospects happen into, whether because they outgrow shortstop or third base or an opening develops there before it does in left field. Oftentimes, first base is just a convenient place to stick another bat. While it's true some players play it better than others, the basic mechanics of the position are pretty adaptable.

So yes, first base is always deep in Fantasy Baseball because it's a repository for big bats. Where those bats start out is another matter.

You won't find many pure first base prospects, then, making this list a bit of a letdown, comparatively speaking. Fortunately, the third overall pick in this past year's draft just so happens to fit the bill.

Note: This list is intended for a variety of Fantasy formats and thus weighs short-term role against long-term value. Not all of these players will contribute in 2020 — most, in fact, will not — but among prospects, they're the names Fantasy owners most need to know.

1. Andrew Vaughn, White Sox

Age (on opening day): 21
Where he played in 2019: Rookie, low Class A, high Class A
Minor-league stats: .278 (205 AB), 6 HR, 17 2B, .832 OPS, 30 BB, 38 K
When a true first baseman with a limited defensive profile gets drafted as high as Vaughn did, you know that bat has some waggle to it. He's a masher, plain and simple, with a strong enough hit tool and batting eye that his value won't be completely tied to his home run total (not that he projects to be lacking there). If you're just looking for production wherever you can get it, prospects don't get much safer than this one.

2. Ryan Mountcastle, Orioles

Age (on opening day): 23
Where he played in 2019: Triple-A
Minor-league stats: .312 (520 AB), 25 HR, .871 OPS, 24 BB, 130 K
A team with something to play for probably would have called up Mountcastle already, but the rebuilding Orioles will have every incentive to play him when they finally do pull the cord, especially now that they seem resigned to the idea of him manning first base. He rates high in quality of contact but has trouble taking a walk, which gives him a profile resembling Nicholas Castellanos.

3. Seth Beer, Diamondbacks

Age (on opening day): 23
Where he played in 2019: high Class A, Double-A
Minor-league stats: .289 (450 AB), 26 HR, 103 RBI, .904 OPS, 46 BB, 113 K
The Astros seemingly struck gold again with by snagging a bat with immediate payoff as late as Pick 28 two years ago, but their willingness to include Beer in the Zack Greinke trade is reason for pause. Anyone who produces like he has all the way into Double-A deserves to be taken seriously, but there are lingering questions about his plate coverage, bat speed and general lack of athleticism.

4. Triston Casas, Red Sox

Age (on opening day): 20
Where he played in 2019: low Class A, high Class A
Minor-league stats: .256 (429 AB), 20 HR, 26 2B, .830 OPS, 58 BB, 118 K
The scouting reports for Casas are sounding an awful lot like Cody Bellinger's at a similar stage of development, meaning he has a swing perfectly tailored for home runs even if the numbers aren't shouting it from the rooftops. He's not on the verge of a major-league assignment yet, but those who can afford to project would be wise to do so here. 

5. Evan White, Mariners

Age (on opening day): 23
Where he played in 2019: Double-A
Minor-league stats: .293 (365 AB), 18 HR, 13 2B, .838 OPS, 29 BB, 92 K
White will show up on basically every top prospects list as a standout defender with a high-floor bat, but he's sort of J.T. Snow throwback in that he may never generate the sort of power needed to stand out at a position replete with it. He did make an effort to elevate the ball more in 2019 and indeed increased his home run output, but when you factor in the decline in doubles, the ISO was still lackluster.

6. Bobby Bradley, Indians

Age (on opening day): 23
Where he played in 2019: Triple-A, majors
Minor-league stats: .264 (402 AB), 33 HR, 23 2B, .912 OPS, 46 BB, 153 K
Major-league stats: .178 (45 AB), 1 HR, 5 2B, .600 OPS, 4 BB, 20 K  
Though he'll technically be DH-only in CBS Sports leagues because of the whiff of major-league action he got in 2019, Bradley fits the traditional first base profile, having been maybe the minors' steadiest power hitter over the past five years. His strikeout rate is off the rails, with seemingly no hope for improvement, but he walks enough that he can maybe hack it as a .235 hitter, in a Rhys Hoskins sort of way. 

7. Lewin Diaz, Marlins

Age (on opening day): 23
Where he played in 2019: high Class A, Double-A
Minor-league stats: .270 (455 AB), 27 HR, 33 2B, .851 OPS, 33 BB, 91 K
Diaz slimmed down and broke out after getting lost in the Twins' lower levels for six years, and after coming over to the rebuilding Marlins in the Sergio Romo trade last July, he has a clear path to the big leagues. Though he doesn't walk much, his respectable contact rate suggests he may have the goods to hack it full-time, provided he keeps the weight off and Marlins Park doesn't zap his newfound power.

8. Kevin Cron, Diamondbacks

Age (on opening day): 27
Where he played in 2019: Triple-A, majors
Minor-league stats: .331 (305 AB), 38 HR, 105 RBI, 1.226 OPS, 61 BB, 77 K
Major-league stats: .211 (71 AB), 6 HR, 4 2B, .790 OPS, 4 BB, 28 K 
Just by being a second-generation player whose brother is himself a full-time big-leaguer, you'd think Cron would get a serious look, but then when you factor in his other-worldly minor-leaguer numbers, where he was the leader in homers despite playing just 84 games, it's a complete travesty he's on the verge of becoming no more than a sad footnote. He's worth keeping around just in case, but if the Diamondbacks were comfortable rolling with Christian Walker over him in 2019, there's no reason to think it'll change.

9. Jared Walsh, Angels

Age (on opening day): 26
Where he played in 2019: Triple-A, majors
Minor-league stats: .325 (382 AB), 36 HR, 30 2B, 1.109 OPS, 59 BB, 115 K
Major-league stats: .203 (79 AB), 1 HR, 5 2B, .605 OPS, 6 BB, 35 K  
Though the Angels have experimented with Walsh as a reliever, he's more likely to make it as a bat and has nothing more to prove in the minors in that regard, having put up numbers nearly as impressive as Cron's last year. He'll have a difficult time breaking in for a team that already has a dedicated DH, but first baseman Albert Pujols is of course old enough to cede at-bats if Walsh proves worthy of them.

10. Roberto Ramos, Rockies

Age (on opening day): 25
Where he played in 2019: Triple-A
Minor-league stats: .309 (431 AB), 30 HR, 27 2B, .980 OPS, 61 BB, 141 K
While the Rockies have several fringy prospects at first base, with Grant Lavigne, Michael Toglia and even Tyler Nevin likely to rank higher on traditional lists, but Ramos is the one knocking on the door today. And the BABIP-boosting potential of Coors Field has the capacity to transform a flawed but veritable slugger into a first-division regular, if the opportunity presents itself. It doesn't hurt that Ramos hit .335 with a 1.033 OPS over the final four months last year.