Tierrasanta Retaining Walls: Ordnance Map, Slide-Prone Ground and Clay

Last Updated: October 27, 2026

In Tierrasanta, a City map of a former artillery ordnance area shapes how a retaining wall footing gets dug, before the soil or the slope even come into it. Batterline offers and manages retaining wall work in Tierrasanta, from repair of older walls to new hillside retaining walls. Building permits come from the City’s Development Services Department, and that map is read alongside the soil and geologic hazard maps before anything is designed.

The City’s mapped ordnance area

The City’s Development Services regulatory map carries a polygon labeled as a former artillery ordnance area, and in a grid sample about 76% of the Tierrasanta planning area falls inside it. No other area this site covers comes close; the next is the neighboring Navajo area at about 1%. On a lot inside the mapped area, the crew digging the footing and drain trench follows “recognize, retreat, report”. So the first look at a lot confirms where it sits on that map.

Slide-prone formations and steep clay slopes

The geologic hazard maps matter as much here as anywhere in the city. In a sample of the City’s Seismic Safety Study layer, 38.8% of Tierrasanta falls in slide-prone formations, the highest share among the areas sampled for this site, and 2.2% in confirmed or possible landslides. Where a lot is in a slide-prone category, a wall over 6 feet from the top of the footing, or a shorter wall holding a surcharge such as a driveway or a fence, needs a geotechnical report before it is designed (SDMC 145.1803). The engineer guide explains how that report feeds the design.

The soil adds its own pressure. A USDA soil survey sample puts moderate or higher shrink-swell at 68% of points, slopes of 15% or more at 65% and of 30% or more at a third, with bedrock within a meter at 40%. The common mapped units are Redding gravelly loam, the Diablo-Olivenhain complex and Friant rocky fine sandy loam on 30 to 70 percent slopes. The City’s standard wall drawings can’t be used on expansive soil or on sites with landslides or slope instability, so many Tierrasanta walls are engineered from the start. Where the slope itself is moving, slope repair comes before or with the wall.

Water on canyon-side lots

About 83% of the yearly rain at both Lindbergh Field and El Cajon falls from November through March (NOAA climate normals), and a wall that drains poorly takes that water as pressure. Gravel and perforated pipe behind the wall, weep holes that stay open and an outlet that doesn’t dump water onto the slope below are the core of retaining wall drainage. The guide to a wall after heavy rain lists what to check.

How a Tierrasanta wall project runs

Half the homes were built before 1980, with a median build year around 1980 (Census ACS), so a wall may be as old as the house behind it. A first visit measures length, exposed height and height from the top of the footing, records the wall type and any lean, bulging or cracks, and checks drains, irrigation, the load above, access and old permits or plans. Then the lot is placed on the ordnance, hazard and soil maps, which decide whether a soils report and an engineer come first. City inspections follow the footing, pre-grout, drainage-before-backfill and final sequence, plus any special inspections an engineered plan calls for. City open permit data (Development Permits approvals) lists 4 Tierrasanta projects with a building permit approval mentioning a retaining wall between January 5, 2024 and October 22, 2026. The permit guide and the cost guide cover the City steps and fees.