Plumbing the depths of the NFL Draft can be dangerous work. There is a fine line between foresight and folly when a team trades down or out of the first round in search of hidden gems.

Consider what happened to the San Francisco 49ers two years ago when they twice traded down in the first round to acquire extra picks.

The 49ers leveraged the 16th overall choice into three picks in 2004. Their reward? Wide receiver Rashaun Woods (first round), cornerback Shawntae Spencer (second round) and linebacker Richard Seigler (fourth round).

It was a decision so bad that it ultimately contributed to the ouster of general manager Terry Donahue and coach Dennis Erickson at season’s end.

How bad was it? Woods, the 31st pick, was a bust and this month was traded. Of the three players drafted, only Spencer remains on their roster.

In the process of moving back in the draft, the 49ers missed a chance at these first-round hits: linebacker D. J. Williams, defensive tackle Vince Wilfork, running backs Steven Jackson and Kevin Jones, and cornerback Chris Gamble.

First-round trades are fraught with risk. Perhaps that’s why Ravens General Manager Ozzie Newsome has dealt his first-round pick only once in the past 10 drafts. That was in 2003, when he sacrificed his 2004 first-round pick to get quarterback Kyle Boller.

Newsome has never traded down in the first round during his time in Baltimore. When he tried to trade up in 2003 for quarterback Byron Leftwich, he was closed out by a faulty phone line at NFL draft headquarters.

Still, Newsome has suggested this might be the year he trades back in the first round, enticed by the prospect of tapping into the deeper vein of first-day talent. It might only take the absence of impact players such as safety Michael Huff (Texas) or nose tackle Haloti Ngata (Oregon) to nudge Newsome out of the 13th pick and into the trade mode.

Or it might take an offer he can’t refuse when another team wants to trade up for, say, quarterback Jay Cutler (Vanderbilt), offensive tackle Winston Justice (USC) or outside linebacker Ernie Sims (Florida State).

Whichever way it goes, Eric DeCosta, the Ravens’ director of college scouting, expects to be on the clock when the decision is made.

“Ozzie’s history has been to wait and see how it develops,” DeCosta said. “At 13, there will be a player we like. I’m comfortable with either scenario (trading down or holding). The only one I’m not comfortable with is to trade up and give picks away.”

The Ravens have only two first-day picks, and more holes than that to fill. They would like to recoup the third-round pick they sent to the New England Patriots a year ago as part of a package to get tackle Adam Terry.

They also could package some second-day picks to move back into the third round (they have eight, including four compensatory picks, which can’t be traded). But it’s their 13th pick overall that represents their most leverage.

Depending on which player drops – and someone always does – the Ravens could get busy fielding phone calls during their 15-minute vigil at 13.

In 2002, the New York Giants, picking 15th, traded up one spot with the Tennessee Titans to ensure they got tight end Jeremy Shockey. The price was their fourth-round pick. General Manager Ernie Accorsi paid it because of his conviction for Shockey.

“I knew for a fact – it has been confirmed since – that somebody was trading with Tennessee to get Shockey,” Accorsi said. “We had to do that.”

Sometimes teams miscalculate trades, too. The same year the Giants got Shockey, the Seattle Seahawks wanted tight end Daniel Graham. Because they also wanted an extra pick, they traded down from 20 to 28.

Bad move. No sooner had they vacated the position than the Patriots jumped up to take Graham with the 21st pick. The Seahawks settled for tight end Jerramy Stevens in the first round and defensive end Anton Palepoi in the second. Stevens has had a suspect career in Seattle and Palepoi is gone.