It was a decision made in the name of safety and predictability. But in the process a natural amenity became an eyesore, a punch line. We love concrete so much in L.A., the old joke goes, that we even paved the river.

Since 32 of the river's 51 miles are within the L.A. city limits, the mayor has a powerful say over its future. The goal should not be to take the river back to some idyllic, preindustrial past. Instead we should look for a few places where we can crack open its hard shell and interact with it in new ways.

ON THE BOULEVARDS: Sunset boulevard

A number of intriguing ideas have already emerged, building on advocacy by the Friends of the Los Angeles River and a master plan the City Council adopted in 2007. Among the most promising is a proposal by landscape architect Mia Lehrer and three architecture firms for the so-called Piggyback Yard, a 125-acre site across the river from Union Station.

It would add walking and biking paths along newly green riverbanks, as well as a park with soccer fields and a botanical garden. It would also act as a powerful pilot project, helping the public see the river's larger potential.

Pushing landowner Union Pacific to sell or make the site available to the city should be high on the next mayor's agenda. So should making sure that the construction of a new Sixth Street bridge, spanning the river between downtown's Arts District and Boyle Heights, stays on pace. The design for that bridge by architects HNTB and Michael Maltzan, which prevailed in an unusually ambitious city competition last year, includes significant new open park space along the river.

There's at least a built-in excuse for our failures to repair the L.A. River: Its massive scale guarantees that any attempt to fix it will be piecemeal.

Not squared away

No such defense can be made of the city's repeated missteps at Pershing Square. The 5-acre park in the heart of downtown is manageably small and self-contained. It is also a perfectly depressing symbol of L.A.'s neglected public realm.

The square was once the most vibrant public space in Los Angeles. The decision to build a parking garage beneath it in the 1950s added entry and exit ramps that cut the square off from the sidewalks around it. A 1993 redesign somehow made that sense of disconnection worse.

Now entertainment giant AEG, the company that brought us L.A. Live, owns the Staples Center and wants to build a pro football stadium downtown, has pledged $700,000 in seed money to reimagine Pershing Square. City Councilmember Jose Huizar, who represents much of downtown, has said that when it comes to a redesign, "everything is on the table."

Here's one thing that shouldn't be: AEG's direct involvement in the revamp, given its track record of sleekly generic architecture and design. The last thing we want to do is turn Pershing Square — not just the city's oldest park but the one with the richest history — into a miniature L.A. Live, ringed with video screens and scrubbed clean of any real sense of place.

The next mayor should write AEG a nice thank-you note and make sure that a redesign task force now being set up is free of the company's influence. And then put everything else back on the table, including ripping out the parking garage that helped doom Pershing Square six decades ago.

Transit's rough surf

When it comes to transportation in Los Angeles, no dream has remained as stubbornly out of reach as a subway to the sea along Wilshire Boulevard. A spur was built to Western Avenue in the 1990s, but by then the rest of the line had been delayed by worries about tunneling in an area with seismic activity and underground pockets of methane gas.

Now the subway has been revived, its financing largely secured by 2008's Measure R sales-tax hike. But obstacles remain. Beverly Hills has fought bitterly to block tunneling beneath its high school.

As the backbone of a thriving new mass-transit system, the subway is worth its admittedly sky-high cost. The subway we build now will be a bargain compared with the one we try to build several decades from now.

And the truth is that opposition in places such as Beverly Hills is not just about safety. (Tunneling of this kind has become routine for subway builders around the world.) It is also driven by fears of the changes a subway line through the city might bring.

The same anxieties kept Bay Area's BART system out of Marin County and the Washington, D.C., Metro out of Georgetown decades ago. (And the subway out of Beverly Hills in the 1980s, for that matter.) If they were patently offensive then, they are indefensible now.

Grand machinations