Horton Plaza in downtown San Diego was...

Horton Plaza in downtown San Diego was the site of two temporary works of public art until Wednesday, when Mario Lara’s strong and elegant “Denominator” proved to be more temporary than he had anticipated.

Lara, one of San Diego’s most accomplished and professionally responsible artists, had fabricated an angular structure of 2-by-4s, painted black and covered with black fabric, which descended the very wide stairway at the western end of the plaza leading to 1st Avenue.

An imposing sculpture rising 14 feet at its highest point and extending halfway down the stairway, it provided a reductive contrast to the surrounding visual clutter, functioning as a noble complement rather than a rebuke to the giddy-gaudiness. It gave pause to visitors and refreshed their eyes as it enhanced the exuberance of its site. It had the effect of a man in a tuxedo accompanying a woman in a party dress.

Unfortunately, the management of Horton Plaza ordered the removal of this beautiful work of art Wednesday morning because of fears that someone might trip on it.

Customer safety is a legitimate issue, but it can also be an excuse for diffusing responsibility while getting rid of something that someone (any complaining employee or visitor) perceives as an affront. (“You call that art?”)

Frankly, many of the planters in Horton Plaza are potential hazards, as are all those stairs and escalators and the light posts and the crotch-high banisters, not to mention baby strollers, wheelchairs and other people, especially little ones.

San Diego is creating for itself a history of rejection of public art. Only the most retardative figurative sculpture seems to find acceptance. We seem to be aiming for the lowest common denominator. And that’s a sad state of affairs.

The other piece at Horton Plaza is Jill Moon’s “Three Yellow Women and a Hat,” a four-element painted wood cutout installed on the roof of Horton Plaza above Wonder Sushi. Moon presented the work in a smaller format earlier this year at Installation Gallery. It is charming and safe. It is scheduled to remain in place until Nov. 15.

Despite the contretemps, the management of Horton Plaza merits kudos for cooperating with David Lewinson in attempting to bring contemporary art to the public. It takes courage and persistence. Plans to reinstall Lara’s work elsewhere in the plaza at a later date are under discussion, according to Lewinson.

The Natalie Bush Gallery (908 E St.) is exhibiting recent wall reliefs by Katherine Hart, as a group enigmatically entitled “You Can’t Get There From Here.”

According to the gallery’s press release, they explore “ideas of uprootedness, stability and changing directions.”

Beats me! But they are satisfying to look at.

Hart has a very secure mastery of composition and, as an artist, reassures our confidence in ourselves as viewers.

It’s a truism that real artists can make art out of anything, including the contents of a vacuum-cleaner bag. Hart doesn’t do that, but she does use some mighty strange objects in constructing her works, including pegboard, chicken wire, heavy-duty saw blades, industrial springs and other found objects whose specialized use is a puzzle to a layman. And that’s as it should be, for Hart compels you to appreciate what she uses on a formal level and to eschew exploration of any residual referentiality.

She obviously enjoys what she’s doing and makes us enjoy it, too. She is not breaking any new ground but she controls the conventions of assemblage with assurance.

The exhibition continues through Dec. 6.

Art Site Gallery (921 E St.), San Diego’s newest alternative art space, has its most important show to date in the fine-art furniture of Bob Niedringhaus and Fred Lanz.

Lanz is represented by a cube table. No matter which way you look at it, you see a red square and a red bar on each side. The horizontal red bar across the top of one side opens as a drawer. Lanz is also showing a group of elegant drawings or proposals for art furniture.

“The show,” Niedringhaus has said, “is based on investigations into the space between applied and fine arts. Some of my tables are like little pieces of architecture.”

Among Niedringhaus’ works are three elegant glass-top tables with pedestals made of sandblasted and spatter-painted Douglas fir 6-by-6s that resemble stone.

A “Bow-Tie” extension table and a “Bow-Tie” cabinet are whimsical but fully, innovatively functional. The table introduces an alternative to the customary seating of diners along the sides of a regular rectangle. The cabinet with its sloping top (and bottom) areas at either end reduces the amount of usable horizontal space, but it looks terrific, and its interior provides storage. (The “Bow-Tie” cabinet will be sold during the Nov. 21 auction benefit for Installation Gallery.)

The exhibition continues through Nov. 29.